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Geological Survey Professional Paper 446
Geology of the Guadalupe Mountains, New Mexico |
STRATIGRAPHY OF PERMIAN ROCKS
FRAMEWORK
The present report area straddles the northwest margin of the Delaware basin,1 one of several sedimentary basins of southwestern United States and northern Mexico which began to form late in Paleozoic time. The Delaware basin reached its maximum depth late in the Permian Period (fig. 3). The Permian rocks of the Northwest shelf, a stable platform area adjacent to the Delaware basin on the northwest, differ markedly in lithology from rocks of the same age in the Delaware basin. A third distinctive facies generally occupies the marginal zone between the shelf and basin facies. In general, the rock units of the basin contain a notably higher proportion of clastic rocks than their equivalents in the shelf area, and the carbonate rocks of the basin have been considerably less dolomitized than the shelf carbonates. The rock units of the basin-margin area contain even fewer clastic beds than equivalent shelf units, but the carbonate rocks of the basin-margin area are intermediate in degree of dolomitization between those of the basin and shelf.
1Originally called the Delaware Mountain Basin by Willis (1929, p. 1034).
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| FIGURE 3.—Map of western Texas and eastern New Mexico and adjacent areas showing positions of some sedimentary basins and uplifted areas that were prominent during Pennsylvanian and Permian time. Map was compiled from various published and unpublished sources. |
The stratigraphic nomenclature of the Permian System in the Delaware basin is almost entirely different from the nomenclature in the adjacent marginal zone and Northwest-shelf area. The different facies are related to one another by their assignment to one or more time-stratigraphic units, or series (fig. 4). The four provincial series of the Permian System in use in Texas and New Mexico are, from oldest to youngest, the Wolfcamp, Leonard, Guadalupe, and Ochoa (Adams and others, 1939, p. 1674). All these series are represented in the Guadalupe Mountains area, although rocks of Wolfcamp age are not exposed at the surface. For ease of description the Permian rocks of the Delaware basin are discussed; this discussion is followed by descriptions of the marginal-zone rocks, and finally by descriptions of the rocks of the Northwest-shelf area. The stratigraphic relations are shown graphically on plate 3.
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| FIGURE 4.—Diagram showing correlation of Permian rock units in Guadalupe Mountains region. Diagonal-lined areas indicate rocks are absent. |
ROCKS OF THE DELAWARE BASIN
The oldest Permian rocks exposed in the Delaware basin in the report area are late Guadalupe in age; the following descriptions of rocks of Wolfcamp, Leonard, and early Guadalupe age in the basin are resumes of published descriptions of those rocks cropping out to the south in Texas, with brief additional notes on their characteristics as determined from nearby drill holes. Rocks of Ochoa age crop out extensively in the southeastern part of the area, but information from drill holes is more useful in their description than that obtained from surface studies.
WOLFCAMP SERIES
WOLFCAMP(?) FORMATION
Rocks of Wolfcamp age in the northern part of the Delaware basin are tentatively assigned to the Wolfcamp Formation of the Glass Mountains in Texas as described by Udden (1917, p. 41) and redefined by P. B. King (1934, p. 727-730). The type Wolfcamp Formation, however, contains a much higher percentage of shale than rocks of the Wolfcamp Series in the northern part of then Delaware basin. P. B. King (1948, fig. 12) used the term Hueco Limestone for the Wolfcamp rocks of the Delaware basin, but because of rather pronounced differences in lithology, it seems preferable to restrict the term Hueco to the approximately time-equivalent rocks of the Northwest-shelf area (fig. 4).
Three drill holes in the Delaware-basin part of the report area have been drilled through the Wolfcamp Series. The series is reported to be 1,490 feet thick in the Union Crawford 1—26 (sec. 26, T. 24 S., R. 26 E.) and 1,730 feet thick in the Gulf Estill 1—AD (sec. 29, T. 24 S., R. 26 E.). In the Humble Wiggs 1 (sec. 31, T. 24 S., R. 27 E.) about 1 mile east of the mapped area, the Wolfcamp Series is about 1,750 feet thick. It consists of about equal amounts of gray, black, or brown shale, and fine-crystalline rarely cherty brownish limestone. A few thin beds of fine-grained gray micaceous and calcareous sandstone are also present. The upper part of the Pennsylvanian sequence is missing in this part of the Delaware basin, and the basal contact of the Wolfcamp Series is an easily recognized unconformity.
LEONARD SERIES
BONE SPRING LIMESTONE
The Leonard Series in the Delaware-basin part of the report area is represented by the Bone Spring Limestone. Originally named the Bone Canyon Member of the Leonard Formation by P. B. King and R. E. King (1929, p. 921-922) and the Bone Springs Limestone by Blanchard and Davis (1929, p. 962) for exposures in the southern part of the Guadalupe Mountains in Texas, the name was changed to Bone Spring Limestone by P. B. King (1934, p. 731).
In the Union Crawford 1—26 (sec. 26, T. 24 S., R. 26 E.) and the Gulf Estill 1—AD (sec. 29, T. 24 S., R. 26 F.), both in the Delaware-basin part of the report area, the Bone Spring Limestone has reported thicknesses of 3,125 and 3,110 feet, respectively, whereas in the Humble Wiggs 1 (sec. 31, T. 24 S., R. 27 E.) just east of the report area, it is apparently nearly 3,400 feet thick. In the Magnolia Homer Cowden 1, 10 miles south of the report area in Culberson County, Tex., the Bone Spring is apparently slightly less than 3,000 feet thick. The formation consists predominantly of brownish-gray fine-crystalline rarely cherty limestone, nearly black to dark-brown shale, and dark-brown shaly limestone. Brownish-gray fine-grained sandstone is abundant in 3 intervals, but it comprises little more than 10 percent of the formation as a whole. As determined from 3 chemical analyses reported by P. B. King (1948, p. 14) and 11 spectrographic analyses and 1 chemical analysis reported by Newell and others (1953, p. 54, 61, 100), the black limestone of the Bone Spring has an average calcite-dolomite ratio of 79:21. Of the samples analyzed, 7 are classified as limestone, 7 as dolomitic limestone, and 1 as dolomite. The 15 samples had an average insoluble residue of 18 percent. Most of the residue consists of silica, but clay minerals and organic material are present.
The Bone Spring Limestone of Leonard age and the underlying rocks of the Wolfcamp Series are lithologically similar and could be considered a single formation. The contact of the Bone Spring Limestone is arbitrarily placed at the base of the lowest thick sandy sequence. On the basis of fusulinids, some paleontologists agree with this choice of lithologic contact, where as others place it on top of the lowest sandy sequence, about 500 feet higher.
GUADALUPE SERIES
DELAWARE MOUNTAIN GROUP
In the Delaware basin the Guadalupe Series is represented by the Delaware Mountain Group made up of the Brushy Canyon, Cherry Canyon, and Bell Canyon Formations in ascending order. Richardson (1904, p. 38) originally named the Delaware Mountain Formation. The formation was raised to group status by P. B. King (1942, p. 575), who first described its constituent formations (p. 577-586).
At the base of the Brushy Canyon Formation is a persistent unit as much as 150 feet thick, composed of dark-gray to black shale and shaly sandstone interbedded with limestone and sandstone. King (1948, p. 16) earlier included this unit with the underlying Bone Spring Limestone and tentatively correlated it with the Cutoff Shale of the basin-margin area, but on the basis of its lithology and additional fossils found in the unit by Newell and others (1953, p. 23), the unit is here included as the basal part of the Brushy Canyon (King, P. B., 1964). Warren (1955, p. 11) referred to the unit as the Pipeline Shale.
At its type locality a few miles south of the present report area the Brushy Canyon Formation above the basal shaly unit consists of 1,000 feet of resistant lenticular coarse-grained sandstone beds separated by less resistant thinner bedded fine-grained sandstone (King, P. B., 1942, p. 578-579). A few thin beds of sandy gray or gray-brown limestone are present. Six spectrographic analyses (Newell and others, 1953, p. 54) show that these limestone beds have an average calcite-dolomite ratio of 73:27 which classifies them as dolomitic limestone. All the samples were high in silica and alumina; carbonate comprised little more than half of the average sample. As P. B. King (1942, p. 587-588) has demonstrated, the Brushy Canyon has no time-equivalent unit in the basin-margin area (fig. 4). Instead, it overlaps onto the arched beds of the underlying Bone Spring Limestone on the Bone Spring monocline (pl. 3).
The Cherry Canyon Formation conformably overlies the Brushy Canyon Formation. At outcrops near the south end of the Guadalupe Mountains in Texas, the Cherry Canyon is about 1,000 feet thick and consists largely of fine-grained sandstone, but it has several named limestone members. These are, from oldest to youngest, the Getaway, South Wells, and Manzanita Limestone Members (King, P. B., 1942, p. 580-581). The Getaway is generally strongly calcitic as determined by five chemical analyses reported by P. B. King (1948, p. 35) and on 1 spectrographic analysis reported by Newell and others (1953, p. 62). Of these, 5 samples are limestone and 1 is dolomite; the average calcite dolomite ratio is 80:20. A single chemical analysis (King, P. B., 1948, p. 36) of the South Wells shows a calcite-dolomite ratio of 5:95, thus determining the sample to be dolomite. The Manzanita is recognized as being strongly dolomitic on the basis of 2 chemical analyses (King, P. B., 1948, p. 37) and 1 spectrographic analysis (Newell and others, 1953, p. 62); it has an average calcite-dolomite ratio of 3:97.
The part of the Cherry Canyon Formation beneath the Getaway Limestone Member extends northeastward across the basin-margin area and grades laterally into the upper part of the San Andres Limestone in the Northwest-shelf area (Boyd, 1955, p. 50; 1958, p. 24-27; Hayes, 1959, p. 2204-2205). The part of the Cherry Canyon between the base of the Getaway and the top of the South Wells grades northeastward into the Goat Seep Dolomite of the basin margin (King, P. B., 1942, p. 588). The part of the Cherry Canyon above the South Wells Limestone Member pinches out over the Goat Seep Dolomite (p. 588). These relations are illustrated on the stratigraphic diagram (p. 3).
The Bell Canyon Formation conformably overlies the Cherry Canyon Formation. Near its type locality a few miles south of the present report area, the Bell Canyon Formation is 700 feet thick (King, P. B., 1942, p. 581). It is similar in lithology to the Cherry Canyon and contains five named limestone members separated by thicker intervals of sandstone. From base to top these limestone members are the Hegler, Pinery, Rader, McCombs, and Lamar. The McCombs was named by Newell and others (1953, fig. 6) and formally defined by P. B. King and N. D. Newell (1956, p. 386-387); the Lamar was named by Lang (1937, p. 874-875); the other limestone members of the Bell Canyon Formation were all established by P. B. King (1942, p. 582-583). In contrast to the limestones of the upper part of the Cherry Canyon, all limestones of the Bell Canyon seem to be strongly calcitic. Based on 6 chemical analyses reported by P. B. King (1948, p. 55-58) and on 2 versenate analyses made for the present report, the limestones of the Bell Canyon show an average calcite-dolomite ratio of 93:7; 7 samples are limestone and 1 dolomitic limestone.
The Bell Canyon grades laterally northwestward into the Capitan Limestone of the basin margin. The transition is accomplished by thickening of the limestone members of the Bell Canyon, gradation of many sandstone beds of the Bell Canyon into limestone of the Capitan, and by pinching-out of some sandstone beds of the Bell Canyon (King, P. B., 1942, p. 590-591). P. B. King (1948) and Newell and others (1953) have presented detailed descriptions of the lithologic characteristics and facies changes of the formations of the Delaware Mountain Group in adjacent areas of Texas.
The only part of the Delaware Mountain Group exposed in the present report area is the top part of the Bell Canyon Formation which crops out discontinuously in low areas southeast of the Reef Escarpment near the New Mexico-Texas State line. The outcrops are of thinly and irregularly bedded dark-gray very fine grained bituminous limestone of the Lamar Limestone Member (fig. 5) overlain by about 5 feet of very thin bedded siltstone and flaggy limestone at the top of the Bell Canyon. In sec. 34, T. 26 S., R. 22 E., these rocks are overlain with apparent conformity by thinly laminated brownish-weathering limestone at the base of the Castile Formation. A small isolated outcrop of thin-bedded limestone, probably the McCombs or Pinery Member of the Bell Canyon, grades into the Capitan Limestone at the mouth of Black Canyon.
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| FIGURE 5.—Thin-bedded dark-gray limestone near top of the Lamar Limestone Member of the Bell Canyon Formation in sec. 34, T. 26 S., R. 22 E. About 1-1/2 miles to the northwest the Lamar Member grades into the breccia member of the Capitan Limestone. |
No fossils were collected from the Bell Canyon Formation during the present investigation. P. B. King (1948, p. 69-75) summarized existing paleontologic knowledge of the formation, and Newell and others (1953, p. 227-232) presented lists of fauna collected from the formation. Skinner and Wilde (1954, p. 435-436; 1955, p. 928-929) have since described four new species of fusulinids from the Lamar Limestone Member and one from the McCombs Limestone Member.
The Delaware Mountain Group has been completely penetrated by three drill holes in the report area. The reported thicknesses of the group in those wells range from 3,408 feet in the Union Crawford 2—27 (sec. 27, T. 24 S., R. 26 E.) to 3,514 feet in the Gulf Estill 1—AD (sec. 29, T. 24 S., R. 26 E.). Most of the limestone members of the Cherry Canyon and Bell Canyon Formations are thin or absent within a few miles from the basin margin, and therefore the formations of the Delaware Mountain Group cannot be separated easily in the strata penetrated in many wells drilled in the basin. Where fusulinid specimens are sufficiently abundant, the contact of the Bell Canyon with the Cherry Canyon can be rather closely picked inasmuch as the genus Parafusulina, present in the Cherry Canyon, is abruptly replaced by the genus Polydiexodina in the Bell Canyon (Williams, 1953, p. 60). Another possible helpful criterion is the degree of dolomitization of the thin carbonate beds of the two formations: the carbonate beds of the Bell Canyon are all apparently relatively pure limestone, whereas those in the upper part of the Cherry Canyon are generally dolomitic. The stratigraphically highest occurrence of abundant relatively coarse grained sandstone and an almost complete disappearance of carbonate cuttings are probably the best criteria for determining the top of the Brushy Canyon Formation in the subsurface. Judging from these criteria the Bell Canyon is about 860 feet thick at the Humble Wiggs 1 well compared to 700 feet near its type locality; the Cherry Canyon is about 1,300 feet thick at the same well compared to about 1,000 feet in its type area; and the Brushy Canyon thickens from 1,000 feet to about 1,340 feet between its type area and the Humble Wiggs 1.
OCHOA SERIES
Rocks of the Ochoa Series are present only in the Delaware basin in the southeastern part of the area and are represented by the Castile and Rustler Formations. Residual remains of the intervening Salado Formation are mapped (pl. 1) with the Castile.
CASTILE FORMATION
The Castile Formation was named by Richardson (1904, p. 43) for Castile Spring, 11 miles south of the present mapped area. The formation underlies most of the area of relatively low relief southeast of the Reef Escarpment (fig. 1), but it is partly covered by surficial deposits and small outliers of the Rustler Formation particularly northwest of Black River.
Because dips are low and topographic relief is slight in the area in which the Castile crops out, and because anhydrite in the formation is weathered to gypsum to depths as great as several hundred feet, outcrops do not show the original composition and thickness of the formation.
The basal beds of the Castile Formation can be seen in outcrops in sec. 34, T. 26 S., R. 22 E., only along the New Mexico-Texas boundary. Here they consist of laminated brownish-gray limestone, a few feet thick, that appears to lie conformably on thin-bedded siltstone and flaggy limestone at the top of the Bell Canyon Formation. These exposures are surrounded by an extensive cover of Quaternary alluvium, and their relations with higher beds of the Castile are not visible.
The lowest part of the Castile in the main outcrop area is exposed on a low west-facing escarpment on the west side of the Yeso Hills from the vicinity of Bottomless Lakes southward beyond the map boundary and in other nearby localities. Here the Castile consists of interlaminated white gypsum and fine-grained dark-brownish-gray limestone (fig. 6).
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| FIGURE 6.—Interlaminated white gypsum and dark-brownish-gray limestone in lower part of the Castile Formation in roadcut in SE1/4 sec. 28, T. 26 S., R. 24 E. |
Individual laminae generally range in thickness from about 1 mm to 1 cm. Local beds of fetid laminated limestone as much as about 6 inches thick are present, but generally each lamina of limestone is separated from the next by a lamina of gypsum. Locally, the laminae are sharply contorted into tight miniature folds. P. B. King (1948, p. 91) suggested that the contortion may be related to certain linear features in the Castile Formation. These features are discussed on page 46 of this report.
Overlying the laminated gypsum and limestone is massive fine-grained white gypsum which in the mapped area is by far the most abundantly exposed type of rock in the Castile. Present in the massive gypsum and the underlying laminated part of the Castile Formation in the Yeso Hills are several low isolated mounds of brown locally laminated limestone. Similar, but usually more prominent, features present in the Castile Formation to the south in Texas were described by Adams (1944, p. 1606, 1622), who termed them "castiles." Most of these castiles contain considerable limestone breccia in addition to the rather massive and laminated limestone. Adams (1944, p. 1622) suggested that the limestone in the castiles replaced gypsum along fractures that opened during hydration of buried anhydrite, and that the "brecciated appearance is due to fragments falling from the walls of the open passages that were later filled with secondary limestone." Previously, several of these limestone mounds in sec. 12, T. 26 S., R. 24 E., were erroneously mapped as outliers of the Rustler Formation (Hayes, 1957).
The stratigraphically highest beds in the Castile Formation are well exposed on the east bank of Black River in the NW1/4 sec. 25, and the NW1/4 sec. 35, T. 24 S., R. 26 E. The rock consists of reddish-brown claystone, siltstone, and sandstone in much-disturbed beds mixed with numerous blocks and broken beds of gypsum (fig. 7). At many other localities brecciated gypsum with a deep reddish stain and a few blocks of reddish-brown siltstone occur beneath outcrops of the overlying Rustler Formation and in sinkholes in the Castile Formation. Although not mapped separately, these breccias, which make up the uppermost 100 to 150 feet of the Castile Formation, are probably a residuum of the Salado Formation whose thick salt beds were almost entirely dissolved by surface and near-surface solution. The red gypsum may be an alteration product of red anhydrite and polyhalite typical of the Salado Formation in the subsurface to the east. The broken beds of clastic rocks probably are insoluble remnants of the many thin clastic beds known to be present in the Salado (Adams, 1944, p. 1609-1610). Locally, in gullies above this brecciated unit are relatively undisturbed beds a few feet thick of gypsum and yellowish-brown siltstone. These beds are overlain with apparent conformity by the basal dolomite member of the Rustler Formation. The gypsum and brown siltstone may be equivalent to the basal part of the Rustler Formation as described by Lang (1938, p. 84) and Adams (1944, p. 1614), but it is here considered residuum of the Salado and included with the Castile Formation.
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| FIGURE 7.—Probable residuum of the Salado Formation on the east bank of Black River in the NW1/4 sec. 35, T. 24 S., R. 26 E. The coarser debris consists of blocks of white and pink gypsum and yellowish-brown and pink siltstone. The matrix is gypsiferous silt. Bank is about 25 feet high. |
All but approximately the top 125 feet of the Castile Formation was penetrated by the McBride Randel 1 well (sec. 7, T. 26 S., R. 26 E.) which was drilled on the Castile outcrop. In this well the basal part of the formation, about 200 feet thick, is interlaminated white anhydrite and gray to brown limestone. Limestone is dominant in the lower part. Above this is a saline sequence 515 feet thick consisting of 275 feet of halite at the base, overlain by 90 feet of laminated anhydrite and limestone and about 150 feet of halite. A 560-foot sequence of anhydrite containing limestone laminae overlies the saline sequence. At the top is 305 feet of white relatively pure anhydrite overlain by 120 feet of white gypsum, which undoubtedly is a surficial hydration product of anhydrite. Thus, the total original thickness of the formation here was at least 1,825 feet, which conforms closely to the thickness of the Castile in wells farther to the east where the entire formation is preserved.
The Castile Formation is quite uniform in lithology over a wide area in the northern part of the Delaware basin, although thicknesses of individual beds vary considerably. The formation changes markedly, however, near the basin margin as is shown in wells a few miles north of the mapped area. The two units of halite thin abruptly about 2 miles from the basin margin, and the limestone content of the laminated anhydrite units decreases greatly in the same area. Very near the basin margin in the Bauerdorf Schrup 1 well (sec. 4, T. 24 S., R. 26 E.) there is no halite and only a trace of limestone in the anhydrite.
The relations of the Castile Formation to rocks of the basin margin are still imperfectly understood. The contact of the Castile with the Capitan Limestone is assumed to be, for the most part, one of sedimentary on-lap, but this is not demonstrable at the surface because the contact of the two units is everywhere covered by surficial deposits. Onlap is suggested by two facts: (a) the highest beds of the underlying Bell Canyon Formation apparently are equivalent to beds high in the Capitan Limestone as first suggested by Lloyd (1929, p. 649) and later verified by detailed work of P. B. King (1948, p. 60) and Newell and others (1953, p. 47); and (b) in subsurface to the east, the Salado Formation gradationally overlies the Castile in the Delaware basin and overlies the Capitan Limestone and equivalent shelf formations outside the basin. Therefore, the time of deposition of the Castile Formation has been presumed to be represented by a disconformity at the base of the Salado Formation outside the Delaware basin. However, a cross section by Jones (1954, p. 108) based on examination of numerous potash test cores from the Salado suggests that the Salado is transitional into the underlying rocks of the shelf area. Newell and others (1953, p. 47) suggested, with reason, that the basal calcareous beds of the Castile are equivalent to the top of the Tansill Formation of the shelf area. Perhaps, as Jones' cross section suggests, most of the Castile Formation is equivalent to the much thinner Fletcher Anhydrite Member at the base of the Salado Formation in the basin-margin area. Until either a transitional or disconformable contact at the base of the Salado Formation in the shelf area can be verified or until the contact of the Castile Formation with the Capitan Limestone can be seen, possibly by trenching, lateral relations of the Castile must be conjectured.
The Castile Formation apparently contains no fossils. It is assigned to the Ochoa Series of the Permian on the basis of its stratigraphic position.
RUSTLER FORMATION
The Rustler was named by Richardson (1904, p. 44) for the Rustler Hills, in Culberson County, Tex.
Only the basal part of the Rustler is preserved in outliers in the report area. It consists of less than 40 feet of thin-bedded grayish-pink fine-crystalline dolomite with abundant spherical vugs as much as 1 cm. in diameter, many of which contain residual gypsum (fig. 8).
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| FIGURE 8.—Thin-bedded dolomite of the Rustler Formation exposed in roadcut in NW1/4 sec. 4, T. 24 S., R. 26 E. |
By the versenate method of analysis, a sample of the dolomite was determined to have a calcite-dolomite ratio of 4:96. These dolomite beds are correlated with the Culebra Dolomite Member which, on the east side of the Pecos River, about 15 miles east of the present report area, is the lowest dolomite in the Rustler (Adams, 1944, p. 1614). In the Rustler Hills of Culberson County, Tex., 28 miles south of the mapped area, several lower dolomite and limestone beds occur in the formation (Walter, 1953, p. 679, 682), but these apparently pinch out before reaching this area.
Along the Pecos River 15 miles to the east, Lang (1938, p. 84) determined a thickness of 500 feet for the Rustler Formation, of which 245 feet lies above the base of the Culebra Dolomite Member. At that locality, more than half of the formation is gypsum and about a third is red, brown, and gray sandstone and siltstone; persistent and conspicuous beds of dolomite make up the remainder.
Fossils are rare in the Rustler Formation, and none were collected in the report area. Because of the poor fossil record, the age of the Rustler was uncertain for many years. Donegan and DeFord (1950) reviewed previous literature on the subject and reported new fossils from the Rustler Hills which indicated a Late Permian age for the formation. Walter (1953) has since substantiated that age assignment on the basis of his collections in the same general area.
ROCKS OF THE BASIN
MARGIN
Permian rocks of the basin-margin facies crop out between Guadalupe Ridge and the base of the Reef Escarpment and in Last Chance Canyon. These rocks are Leonard and Guadalupe in age. The Wolfcamp and lower part of the Leonard Series in the basin-margin facies have been penetrated at a few places in the area by drilling and are exposed to the south in Texas. Rocks of the Ochoa Series have been removed by erosion from all but the Delaware basin in the report area.
WOLFCAMP SERIES
The margin of the Delaware basin apparently was not as well defined during Wolfcamp time as it was during Leonard and Guadalupe times, and no distinctive marginal facies of Wolfcamp rocks has been identified definitely. Presumably, the dark shale and limestone sequence of Wolfcamp age in the Delaware basin grades laterally over a broad transition zone into all but the uppermost part of the lighter colored dolomite and greenish-gray shale sequence of the Hueco Limestone of the Northwest-shelf area. The 1,160 feet of rock ascribed to the Wolfcamp Series in the Union White 1 well (sec. 17, T. 24 S., R. 22 E.) apparently represents the shelfward part of this broad transition zone. In this well most of the series is represented by fine-crystalline light- to dark-gray dolomite containing minor amounts of gray, brown, green, and black shale, whereas the basal 180 feet or so of the sequence is predominantly light- to dark-gray limestone. The transition between the Hueco Limestone of the shelf and the Wolfcamp rocks of the basin is apparently located farther to the northwest (shelfward) in the basal part of the series than it is in the upper part. There is some suggestion of this in the Union White 1 and a general southeastward migration of the basin margin is well displayed in later Permian rocks of the Guadalupe Mountains.
LEONARD SERIES
VICTORIO PEAK LIMESTONE
The Bone Spring Limestone of the Delaware basin grades laterally northwestward into the Victorio Peak Limestone which was originally named the Victorio Peak Massive Member of the Bone Spring Limestone by P. B. King and R. E. King (1929, p. 921) for exposures in the Sierra Diablo. Because it is a distinct mappable unit, the Victorio Peak is now classified as a separate formation (King, P. B., 1964). Relations between the Victorio Peak and Bone Spring of the Delaware basin cannot be observed in the report area, but exposures in the Texas part of the Guadalupe Mountains were described by P. B. King (1948, p. 26-27), who wrote:
During the last half of Leonard [Bone Spring] time, the gray Victorio Peak * * * was spread out on the shelf area, extending as far southeastward as the edge of the Delaware Basin, where it apparently intergraded with black limestone. During the first half of Leonard time, black limestones extended for several miles farther northwestward toward the shelf, underneath the gray Victorio Peak beds. In the Guadalupe Mountains, exposures of the black limestone do not extend deeply enough to indicate their relations to the shelf area.
Subsurface data indicate that the black limestone beds of the Bone Spring do not extend as far northwest as the Union White 1 well (sec. 17, T. 24 S., R. 22 E.). Instead, they apparently grade northwestward into the light-gray dolomite beds of the basal part of the Victorio Peak Limestone and, possibly, into the uppermost part of the Hueco Limestone, assuming the upper part of the Hueco of the Hueco Mountains is Leonard in age, as has been suggested (King, P. B., King, R. E., and Knight, J. B., 1945; Bachman and Hayes, 1958, fig. 5).
P. B. King (1948, p. 17-18, 164) recognized three informal divisions of the Victorio Peak in its exposures on the west side of Cutoff Mountain south of the New Mexico-Texas State line. The incompletely exposed lower division consists of gray fine-grained somewhat dolomitic limestone in 1- to 6-foot beds. It contains rare small chert concretions. The middle division, 117 feet thick, consists (p. 18) "of slope-making, thin-bedded, light-gray or white limestone, with much buff, fine-grained, calcareous sandstone interbedded." The upper division consists of gray fine-grained limestone in beds as much as 7 feet thick in its basal 217 feet and of thin-bedded limestone in the top 25 feet.
The lower and middle divisions of the Victorio Peak Limestone presumably grade northwestward into the Yeso Formation, whereas the upper division of the Victorio Peak probably grades into the basal part of the San Andres Limestone (pl. 3). The southeasternmost occurrence of gypsum in the Yeso Formation is arbitrarily used as the dividing line between shelf and basin-margin terminology.
CUTOFF SHALE
Overlying the Victorio Peak Limestone, except where truncated by erosion over the Bone Spring monocline (pl. 3), is the Cutoff Shale. Named the Cutoff Shaly Member of the Bone Spring Limestone by P. B. King (1942, p. 569-570) for exposures on Cutoff Mountain a few miles southwest of the present report area, the unit is now given formational status (King, P. B., 1964). The Cutoff is composed of thin-bedded limestone interbedded with dark siliceous shale, sandy shale, and soft-weathering sandstone. It is tentatively correlated with the uppermost part of the Bone Spring Limestone or the lowest part of the Brushy Canyon Formation of the Delaware-basin facies and is assigned a Leonard or Guadalupe age or both (Hayes, 1959, fig. 7). The Cutoff grades laterally northwestward through a broad transition zone into part of the main body of the San Andres Limestone. This transition is not exposed in the present report area, but it was described by Boyd (1958, p. 14) as occurring in the Brokeoff Mountains a few miles to the west.
GUADALUPE SERIES
SANDSTONE TONGUE OF THE CHERRY CANYON FORMATION
The lowest rocks of Guadalupe age in the basin margin area are included in the sandstone tongue of the Cherry Canyon Formation which disconformably overlies the Cutoff Shale. The Brushy Canyon Formation of the Delaware basin is represented by the disconformity (fig. 4; pl. 3). First described by Baker (1920, p. 114) and later by others (Darton and Reeside, 1926, p. 423; Crandall, 1929, p. 935; Lang, 1937, p. 859), the sandstone tongue of the Cherry Canyon Formation was named by P. B. King (1942, fig. 7; 1948, p. 38). As defined by P. B. King (1948, p. 38, 47), the tongue is a northward (shelfward) extension of the lower fourth (or sub-Getaway part) of the Cherry Canyon Formation and persists as a layer 200 to 300 feet thick beneath the Goat Seep Dolomite which interfingers with the upper three-fourths of the Cherry Canyon. Boyd (1955, p. 50; 1958, p. 14) later demonstrated the shelfward transition of the sandstone tongue of the Cherry Canyon Formation into the upper part of the San Andres Limestone (fig. 9).2
2Boyd believed that the uppermost part of the sandstone tongue of the cherry canyon Formation was transitional into the lower part of the Grayburg Formation; but, for reasons discussed on p. 29, I have used an upper boundary for the San Andres Limestone, which is considerably higher stratigraphically than that used by Boyd, thus making the sandstone tongue of the Cherry Canyon equivalent only to part of the San Andres.
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| FIGURE 9.—Lateral facies boundaries of some stratigraphic units of Guadalupe age in the report area. |
The only exposures of the sandstone tongue of the Cherry Canyon Formation in the report area are in the walls of Last Chance Canyon and in three tributaries in the southern part of T. 23 S., R. 22 E., and the northern part of T. 24 S., R. 22 E. These exposures were correlated with the Cherry Canyon by P. B. King (1942, fig. 7), and this correlation has been generally accepted (Stipp, 1951; Boyd, 1958, p. 26) on the basis of stratigraphic relations, lithology, and fossils.
The tongue is 264 feet thick in Last Chance Canyon near the mouth of Sitting Bull Canyon (stratigraphic section 9, pl. 3). Here it consists of moderately resistant indistinctly bedded grayish-orange very fine grained well-sorted quartz sandstone with scattered irregular chert nodules and silicified megafossils. Some of the chert nodules include abundant silicified fusulinids. The upper 25 to 30 feet of the unit is transitional into an overlying dolomite tongue of the San Andres Limestone. Darton and Reeside (1926, p. 426) listed 35 species of fossils, including 18 different kinds of brachiopods, that were collected from the sandstone tongue of the Cherry Canyon Formation from a locality near stratigraphic section 9 (pl. 3). P. B. King (1948, p. 47-48) and Boyd (1958, p. 61-62) discussed fossils from the unit elsewhere in the Guadalupe Mountain region. No specimens of unreported fossil species were collected from the sandstone tongue of the Cherry Canyon Formation during the present investigation.
GOAT SEEP DOLOMITE
Gradationally overlying the sandstone tongue of the Cherry Canyon Formation in the basin-margin area is the Goat Seep Dolomite. The Goat Seep is exposed only as an inlier in North McKittrick Canyon near the southwest corner of the mapped area, and neither the base of the formation nor its relations with equivalent rocks of the Delaware basin can be seen. P. B. King (1942, p. 588) named the Goat Seep and stated that:
the Getaway and South Wells limestone members of the Cherry Canyon formation thicken northward, and the intervening sandstones disappear * * * [the limestone members] coalesce into a solid mass, here termed the Goat Seep limestone * * *. The Manzanita limestone member and associated sandstones, which lie above the Getaway and South Wells members, pinch out northward, leaving only a sandy zone between the Goat Seep and the overlying Capitan limestone.
The lower, or Getaway equivalent, part of the Goat Seep is thick bedded and the upper part massive. Although P. B. King (1948, p. 40) extended the name Goat Seep to include equivalent thin-bedded limestones and interbedded sandstones that lie shelfward, Newell and others (1953, p. 42-43) restricted the term Goat Seep to the massive "reef and forereef talus facies" of the basin margin. This lateral restriction of the Goat Seep was followed by Boyd (1958, p. 15) and is used in the present report. Because the Goat Seep consists dominantly of dolomite rather than limestone, it is referred to as the Goat Seep Dolomite here.
The upper 500 feet of the Goat Seep Dolomite is exposed in North McKittrick Canyon. It consists mostly of light-gray massive fine-crystalline to saccharoidal dolomite which at places is very porous and has a worm-eaten appearance. Forty-two thin sections of Goat Seep from a stratigraphic section measured at this locality were examined, but the rock has been so thoroughly dolomitized that little primary structure was seen. In some thin sections microbrecciation is visible, and in others, shadowy remnants of unidentifiable fossils are present. A few sections contained as much as 25 percent scattered very fine quartz grains.
Calcite-dolomite ratios of 11 samples of the Goat Seep from the section measured in North McKittrick Canyon were determined by the versenate method. These ranged from 26:74 to 3:97 and averaged 9:91. Of the samples analyzed, 8 are classified as dolomite and 3 as calcareous dolomite. These ratios are similar to ratios of 3:97 and 1:99 calculated from a previously reported chemical analysis (King, P. B., 1948, p. 40) and spectrographic analysis (Newell and others, 1953, p. 110).
No fossils were collected from the Goat Seep during the present investigation. P. B. King (1948, p. 48-50) summarized earlier paleontologic studies of the formation. Newell and others (1953, p. 227-232) presented a fossil list showing 142 forms from the unit, and Boyd (1958, p. 83) listed a few additional forms. Brachiopods are predominant in the lists. Kenji Konishi (oral communication, 1960), of the Geological Survey, identified the algae Solenopora sp., Mizzia sp., and Gyroporella? sp. and noted unidentifiable forms of stromatolites in thin sections of rocks from North McKittrick Canyon.
CAPITAN LIMESTONE
The upper part of the Guadalupe Series in the basin margin area is represented by the Capitan Limestone which crops out in a continuous band along the Reef Escarpment across the southeastern part of the mapped area. The Capitan was named by Richardson (1904, p. 41) for exposures at the south end of the Guadalupe Mountains, 8 miles south of the present report area. The boundaries of the Capitan were not defined by Richardson, and some early workers apparently included the Goat Seep Dolomite and the bedded carbonate rocks of the Artesia Group of the Northwest shelf in the formation (Girty, 1908, p. 7; Lloyd, 1929, p. 649). Baker (1920, p. 114) recognized that the Goat Seep was a distinct unit and Darton and Reeside (1926, p. 419) separated rocks that are now included in the Artesia Group. The limits of the Capitan as used by Crandall (1929, p. 933, 938) and by Lang (1937, p. 863) have been used by most of the more recent workers (King, P. B., 1948, p. 59; Adams and Frenzel, 1950, p. 296; Newell and others, 1953, p. 15), and are used in this report. The formation is thoroughly described in the papers cited above, and only some of the general features are given in the present paper.
The oldest part of the Capitan Limestone rests on the underlying Goat Seep Dolomite with an indistinct but apparently disconformable contact. The disconformity represents the uppermost beds of the Cherry Canyon Formation of the basin (King, P. B., 1948, p. 38; Newell and others, 1953, p. 28) and, possibly, the uppermost part of the Queen Formation of the shelf. Within the mapped area, the basal contact is exposed only in the upper part of North McKittrick Canyon. The youngest part of the Capitan has been removed by erosion in the report area, but it is overlapped by evaporite deposits of the Ochoa Series in the subsurface east of Carlsbad. In the report area, the Capitan Limestone grades laterally southeastward into the Bell Canyon Formation and, possibly, into the lowermost beds of the Castile Formation (fig. 9). This transition is incompletely displayed near the mouth of Big Canyon and can be seen more completely at the mouth of McKittrick Canyon 1-1/2 miles south of the mapped area. The Capitan grades laterally northeastward into the Seven Rivers, Yates, and Tansill Formations of the Artesia Group, as shown at numerous places within the mapped area.
The Capitan Limestone is divided into two units, a massive member and a breccia member. The two grade into one another both laterally and vertically (fig. 27). The gradational contact between these two members rises in stratigraphic position from northwest to southeast and is depicted approximately on the geologic map (pl. 1). The members correspond to the "reef" and "reef talus" facies, respectively, of Newell and others (1953, fig. 24), but descriptive rather than genetic terms for the facies are used in this report.
The massive member of the Capitan Limestone is characterized by a virtual absence of bedding planes. It holds up nearly vertical cliffs in canyon walls from Big Canyon to Slaughter Canyon (fig. 10). It is composed almost entirely of very light gray to yellowish-gray fine-textured limestone which weathers light olive gray (fig. 11). Isolated aggregates of white coarsely crystalline calcite are locally common. Calcite-dolomite ratios computed from 11 spectrographic analyses reported by Newell and others (1953, p. 110), 2 chemical analyses reported by P. B. King (1948, p. 62), and 2 versenate analyses made during the present work range from 99:1 to 84:16 and average 96:4. Of these samples, 14 are limestone and 1 is dolomitic limestone. Sandstone dikes and isolated pockets of sandstone are common at many localities and are of two ages. Nearly vertical quartz pebble-bearing sandstone dikes near the top of the Capitan in some canyons are clearly of post-Capitan age and are discussed on page 37. Irregularly branching dikes as much as several inches thick and isolated pockets contain very fine grained sandstone that is similar in lithology to sandstone in the Yates and Bell Canyon Formations. Sandstone in these irregular dikes and pockets is almost certainly of Capitan age and apparently fills original voids in the limestone. The dikes rarely extend more than a few tens of feet in any direction, but they are common throughout the massive member. They are especially numerous about half a mile upstream from the mouths of Rattlesnake and Slaughter Canyons.
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| FIGURE 10.—Northeast side of Slaughter canyon at location of stratigraphic section 17. Lateral transition of parts of the Yates (Pya) and Tansill (Pt) Formations into the massive member of the Capitan Limestone (Pcm) and transition of the massive member to the breccia member of the Capitan (Pcb) take place here. Gravel (Qg) covers bottom of canyon. |
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| FIGURE 11.—Photomicrograph of limestone from the massive member of the Capitan Limestone. Solution cavity in lower right is partially filled by crystalline calcite which has apparently replaced some of the cavity wall. Most of the rock is finely divided "lime-mud" which may contain a trace of carbonaceous material. Light areas are autoclasts of limestone within the fine matrix. Fossil at upper left may be part of the brachiopod Prorichthofenia or Leptodus. Arrow 1 mm long points up. |
The massive member of the Capitan Limestone is interpreted to be a reef deposit made up of the remains of marine organisms; however, upon cursory examination it seems to be only sparsely fossiliferous at most places. Solution and recrystallization, surficial weathering, and the very small size of many of the fossils make the fossils difficult to recognize in the field. Small profusely fossiliferous patches of rock can be found, however. One of these is in the upper part of the member on the south side of Yucca Canyon in SE1/4 sec. 28, T. 25 S., R. 23 E. Other fossiliferous patches were seen in West Slaughter and Rattlesnake Canyons. Newell and others (1953, p. 227-232) compiled a list of at least 115 species of fossils from the Capitan. Included are 5 species of fusulinids, 14 species of sponges, 3 species of corals, crinoid remains, 12 species of bryozoans, 46 species of brachiopods, 33 species of mollusks, and 1 species of trilobite. In addition, Johnson (1942) identified six species of fossil algae which apparently were collected from the massive member of the Capitan Limestone, and Newell and others (1953, pls. 17, 18) illustrated three other species of algae not reported by Johnson. Kenji Konishi (oral communication, 1960), of the Geological Survey, examined collections from the Capitan made during the present investigation, and found, besides several species that had been described earlier, specimens of Mizzia sp. from the massive member and Permocalculus? sp. from the breccia member. In all, 3 species of the coralline algae Solenopora, 2 species of the calcareous colonial algae Collenella, and 6 species and 4 genera of green algae have been described from the Capitan. In total volume, stromatolites are probably the most important fossil in the unit, but Newell and others (1953, p. 112) also consider chambered calcareous sponges and other forms as being important "frame-building" organisms.
A transitional contact between the massive member of the Capitan Limestone and the bedded dolomite and sandstone of the upper part of the Artesia Group rises in stratigraphic position from northwest to southeast. Thus, the transition of the base of the Capitan into the basal part of the Seven Rivers Formation is between 2 to 3 miles northwest of its transition into the Tansill Formation. Details of the transition are described in the discussion of the Artesia Group.
The transition of the massive member or "reef rock" of the Capitan into the breccia member or "reef talus" also progresses stratigraphically upward toward the southeast (pls. 1, 3; fig. 9). In vertical sections the thickness of the massive member ranges from about 250 feet to as much as 750 feet and averages about 400 feet (pl. 3).
In the field the breccia member of the Capitan Limestone is distinguished from the massive member primarily by differences in bedding and resistance to erosion. Whereas the massive member is for the most part unbedded, the breccia member is made up of thick beds that dip southeastward 20° to 30° or more. The massive member generally holds up nearly vertical smooth-weathering cliffs; the breccia member generally forms ragged slopes (fig. 10). The contact between the two members of the Capitan is vague and is mapped where indistinct bedding planes of the breccia member flatten upward and fade out into the massive member. As much as 5° to 10° of the dip in the breccia member probably is due to post-Permian structural movements, but the remainder is depositional.
The breccia member at many places contains coarse angular cobbles and boulders of limestone and dolomite derived from the massive member and from bedded dolomites of the upper part of the Artesia Group. It contains in addition rare fragments of sandstone that may also have been derived from the Artesia Group. Most of the breccia member, however, is microbreccia derived from the same sources (fig. 12). Because it contains both fragments of limestone from the massive member and dolomite from the Artesia Group, calcite-dolomite ratios of the breccia member are much more variable than in the massive member. Ratios for 14 calcite-dolomite samples were computed from 2 chemical analyses reported by P. B. King (1948, p. 62), 3 spectrographic analyses reported by Newell and others (1953, p. 69), and 9 versenate analyses made during the present investigation. These ratios range from 99:1 to 2:98 and average 60:40. Among the samples tested, 3 are limestone, 5 are dolomitic limestone, 4 are calcareous dolomite, and 2 are dolomite.
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| FIGURE 12.—Photomicrograph of limestone from the breccia member of the Capitan Limestone. Note broken fragments of large fusulinids (probably Polydiexodina) and other organic debris in finely crystalline calcite matrix. At top are subrounded limestone clasts derived from the massive member. Bar is 1 mm long. |
Basinward transition of part of the breccia member of Capitan Limestone into the Bell Canyon Formation can be observed near the mouth of Big Canyon in the report area. This transition has been described in detail by P. B. King (1948, p. 59-61) and by Newell and others (1953, p. 67-69) on the basis of more complete exposures to the south in Texas. The contact between the Capitan and Bell Canyon on the geologic map (pl. 1) represents the disappearance northwestward of sandstone beds of the Bell Canyon into limestone breccia. In the words of P. B. King (1948, p. 61) the sandstone disappears "partly by interfingering with numerous limestone tongues and partly by a change into sandy limestone and thence into pure limestone." At approximately the same lateral position a less abrupt change in the bedding, texture, composition, and color of the limestone takes place. Steeply inclined thick beds of light-gray limestone and dolomite of the breccia member become thinner where they flatten out and change to darker gray bioclastic limestone of the Bell Canyon Formation. As was mentioned above, the youngest beds of the Capitan may grade into the basal laminated limestone beds of the Castile Formation, but this cannot be proved by the present exposures. The Capitan to Bell Canyon transition takes place in progressively younger beds toward to southeast.
The maximum vertical thickness of the breccia member measured across its inclined beds without regard to the dip is probably about 1,750 feet, and its average thickness is about 1,250 feet. The breccia member of the Capitan comprises about two-thirds of the total bulk of the formation (pl. 3). The maximum vertical thickness of the Capitan Limestone as a whole may reach 2,000 feet in McKittrick Canyon about 1 mile south of the present report area (King, P. B., 1948, p. 61).
A few miles north the Capitan Limestone is covered by younger rocks. Its presence along most of the margin of Delaware basin is established from well data and from outcrops in the Glass and Apache Mountains in Texas.
ROCKS OF THE NORTHWEST
SHELF
Permian rocks of Wolfcamp, Leonard, and Guadalupe age of the Northwest shelf are found in the northwestern part of the report area; rocks of Ochoa age are not preserved. The basal Permian formation of the shelf, the Hueco Limestone, is not exposed at the surface, and the lower part of the overlying Yeso Formation is also buried. The following descriptions of those units are based primarily on subsurface data.
HUECO LIMESTONE
The oldest rocks of definite Permian age of the shelf facies are assigned to the Hueco Limestone. The term Hueco was originally used by Richardson (1904, p. 32-38) for a thick sequence of rocks exposed in the Hueco Mountains, Tex. The sequence later proved to include rocks ranging in age from Devonian to Permian and the name Hueco was formally restricted by P. B. King (1934, p. 742) to apply only to Permian rocks. The Hueco is known only in the subsurface of the report area; the nearest surface exposures are 50 miles south in the Sierra Diablo and 55 miles west in the Hueco Mountains (fig. 2). Two distinct members of the formation are recognized in the report area.
Where both are present, the lower member of the Hueco Limestone is lithologically indistinguishable from the uppermost strata of Pennsylvanian age, but they usually can be separated on the basis of the fusulinids present. The lower member of the Hueco is similar in age and lithology to the type Bursum Formation of south-central New Mexico as originally defined by Wilpolt and others (1946) and to the Laborcita Formation of Otte (1959) in the northern Sacramento Mountains (fig. 2), but it is probably not coextensive with either of those units. The member consists of medium-gray fine-crystalline locally siliceous limestone interbedded with reddish-brown, greenish-gray, and gray shale and minor amounts of fine-grained sandstone.
The thickness of the lower member of the Hueco varies considerably over short distances. In the Continental-Standard of Texas Bass 1 well (sec. 5, T. 22 S., R. 21 E.) on Texas Hill, the lower member of the Hueco and the underlying Pennsylvanian sequence are absent. The lower member of the Hueco is apparently present in most wells in the shelf area, however, and reaches a maximum thickness of at least 500 feet in the Magnolia State "W" 1 (sec. 16, T. 21 S., R. 22 E.).
The upper member of the Hueco consists chiefly of medium-gray fine-crystalline dolomite, subordinate greenish-gray shale, and rare grayish-red shale. The proportion of red shale probably increases northwestward toward the Sacramento Mountains where the Hueco grades laterally into red beds of the Abo Sandstone (Pray, 1954, p. 101; Bachman and Hayes, 1958, p. 692).
The thickness of the upper member of the Hueco Limestone ranges from about 880 feet in the Continental-Standard of Texas Bass 1 well, where the lower member of the formation and Pennsylvanian rocks are absent, to about 1,330 feet in the Continental East Texas Hill 1 (sec. 1, T. 22 S., R. 21 E.). It is probably even thicker in the Humble Huapache 2 (sec. 23, T. 23 S., R. 22 E.).
Much of the Hueco Limestone is laterally equivalent to rocks of the Wolfcamp Series of the Delaware basin, but the uppermost part is probably equivalent to the basal part of the Bone Spring of Leonard age. This is apparently true in the Hueco Mountains (King, P. B., and others, 1945), and it may also be true in the southern part of the Sacramento Mountains (Bachman and Hayes, 1958, p. 695). Where the upper part of the Hueco Limestone of the shelf grade southeastward into rocks of the basin, the Hueco contains thick fine- to coarse-crystalline dolomite beds which are in formally referred to as "Abo reefs" (Podpechan, 1959; LeMay, 1961). These rocks contain large reserves of petroleum in fields to the north and northeast of the report area.
YESO FORMATION
The Yeso Formation was named by Lee (1909, p. 12) for exposures on Mesa del Yeso, 150 miles northwest of the present report area. Darton (1922, p. 181) reduced the Yeso to a member of the Chupadera Formation, but it was redescribed and again raised to formational status by Needham and Bates (1943, p. 1657-1661).
Rocks assigned to the Yeso Formation in the report area are actually in a transition facies between the Victorio Peak Limestone and the much more gypsiferous Yeso Formation of areas to the north. These transition rocks could just as well be assigned to the Victorio Peak; but where even thin beds of gypsum or anhydrite are present, they are arbitrarily placed in the Yeso.
The upper 600 feet or so of the Yeso Formation crops out on the lower slopes of Algerita Escarpment and is the oldest rock exposed in the report area. The major constituent of the Yeso Formation in these exposures is dark- to light-gray generally slightly fetid dolomite and dolomitic limestone mostly in beds less than 1 foot thick. Two versenate analyses of carbonate samples from the Yeso showed calcite-dolomite ratios of 6:94 and 10:90. Interbedded with the dolomite in about equal amounts are massive white gypsum and thin beds of nonresistant grayish-yellow sandy quartzose siltstone. The percentage of gypsum and siltstone in the Yeso decreases notably from northwest to southeast along the outcrop. At the north end of the outcrop band the top of the Yeso is a bed 8 to 10 feet thick of sandy siltstone which is conformably overlain by relatively thick-bedded cherty dolomite at the base of the San Andres Limestone. Toward the south, the siltstone is missing and dolomite of the Yeso Formation is directly overlain by dolomite of the San Andres Limestone. A graphic section of the upper part of the Yeso Formation as it appears in the central part of its outcrop band is shown on plate 3 (stratigraphic section 1).
The sandy siltstone bed that occurs at the top of the Yeso Formation in the northern part of the outcrop was considered by Skinner (1946, p. 1864) to be a southern extension of the Glorieta Sandstone of central New Mexico. However, it appears that the Glorieta pinches out near Sierra Blanca, about 75 miles to the northwest (R. L. Harbour, oral communication, 1958), and because the siltstone bed closely resembles other siltstone beds in the Yeso, it is here included as a part of the Yeso Formation. It is a possible equivalent of siltstone at the top of the Yeso in the subsurface at Dunken Dome, less than 25 miles to the northwest, which Needham and Bates (1943, p. 1660) correlated with the Joyita Sandstone Member of the Yeso.
The thickness of the Yeso varies in wells drilled in the area. In general, the formation is thinnest where the underlying Hueco Limestone is relatively thin, and the Hueco is thinnest over areas where the Pennsylvanian sequence is thin or absent. In the Continental-Standard of Texas Bass 1 (sec. 5, T. 22 S., R. 21 E.) where Pennsylvanian rocks are absent and the Hueco Limestone is relatively thin, the Yeso is about 1,685 feet thick. In the Magnolia State "W" 1 (sec. 16, T. 21 S., R. 22 E.) where both the Pennsylvanian sequence and the Hueco Limestone are relatively thick, the Yeso is about 2,410 feet thick. It is apparently even thicker in the Humble Huapache 2 (sec. 23, T. 23 S., R. 22 E.) where the Pennsylvanian System reaches its maximum thickness in the area. It appears that the crustal movements that affected Pennsylvanian sedimentation were still active in Yeso time. Similar conclusions were drawn by Pray (1959, p. 126) on the basis of work in the Sacramento Mountains.
In the subsurface the Yeso Formation consists dominantly of medium- to light-gray fine-crystalline dolomite. In most wells small amounts of white to very light gray anhydrite are present in the upper 200 to 250 feet of the formation. Very light gray coarse quartzose siltstone and very fine grained sandstone occur in many thin layers and in two relatively thick layers, but they make up less than 10 percent of the whole unit. The siltstone sequence at the top of the Yeso noted in outcrops is also a useful subsurface datum. It apparently ranges from as little as 10 feet to more than 60 feet thick. Another thick siltstone and sandstone sequence is 1,150 feet below the top of the Yeso in the Continental-Standard of Texas Bass 1 where the formation is 1,685 feet thick. In the Magnolia State "W" 1, where the formation is 2,410 feet thick, this siltstone occurs 1,830 feet below the top of the formation (pl. 2). It is locally at least 100 feet in thickness and probably represents the subsurface Drinkard Sandy Member of R. E. King (1945, p. 13), which he believed was present in a well in sec. 16, T. 21 S., R. 23 E., only 6 miles east of the Magnolia State "W" 1. The Drinkard Sandy Member of King (1945) is stratigraphically too low in the Yeso to be exposed in the report area, and it has apparently never been identified in outcrops. In wells, the Yeso is distinguished from the underlying Hueco Limestone by a lack of greenish-gray and reddish-brown shale and the presence of sandstone and siltstone beds.
Lateral transition of the Yeso Formation into the Victorio Peak Limestone cannot be seen in outcrops; so the precise relation of the two units is unknown. However, because the uppermost part of the underlying Hueco Limestone may be equivalent to the basal part of the Bone Spring, and because, as is described below, the basal part of the overlying San Andres Limestone may be equivalent to the upper division of the Victorio Peak, the Yeso Formation is presumed to be equivalent to all but the youngest and oldest beds of the Victorio Peak.
The Yeso Formation is nearly devoid of recognizable fossils. Dolomitized fusulinids are present in some beds, and Boyd (1958, p. 19) noted crinoid columnals in the Yeso in the El Paso Gap quadrangle at the southern end of the outcrop band in Big Dog Canyon.
SAN ANDRES LIMESTONE
The San Andres Limestone is widely exposed in the Guadalupe Mountains upland, in and near the Brokeoff Mountains in the northwestern part of the area, and in several inliers, the most important of which is in Last Chance Canyon in the central part of the area. Originally named by Lee (1909, p. 12) for the San Andres Mountains, 100 miles to the west, the San Andres was reduced to a member of the Chupadera Formation by Darton (1922, p. 181), but it was redescribed and reelevated to formational status by Needham and Bates (1943, p. 1664-1666).
The San Andres Limestone is divided into two in formal units: a lower cherty member and an upper member. Boyd (1958, p. 23) recognized a similar division in the Brokeoff Mountains (fig. 1), but he was uncertain whether the upper limit of abundant chert defined a single stratigraphic horizon. In Last Chance Canyon the two members are distinctive and are separated by a local unconformity. Farther north and west, however, the contact is apparently conformable and indefinite. Reconnaissance north of the mapped area (Hayes, 1959, p. 2199-2200) indicates that the stratigraphically highest occurrence of abundant chert does not form a consistent regional time datum; it is, nevertheless, a fairly consistent datum in the report area, and it seems to be a useful subsurface datum within 20 or 30 miles north and west of the basin margin. Where the formation is complete, the two members of the San Andres are approximately of equal thickness.
The lower cherty member of the San Andres northwest of the Last Chance Canyon-Rocky Arroyo drainage divide is characterized by variable amounts of rusty-weathering light- to medium-gray chert that generally occurs in irregularly shaped nodules but at some places is found as thin lenticular beds. Many of the chert nodules have indistinct margins and contain patches of dolomite, whereas other nodules seem to consist of pure chert which has sharply defined margins. Chert is most abundant near the top of the member where it locally comprises more than one-fourth of the rock.
The bulk of the lower cherty member in the northwestern part of the area is dolomite and dolomitic limestone. As determined from 8 versenate analyses made during the present investigation and a spectrographic analysis reported by Boyd (1958, p. 24), calcite-dolomite ratios of carbonate rock in the member range from 0:100 to 73:27 and average 16:84. Of the samples analyzed, 5 are classed as dolomite, 3 as calcareous dolomite, and 1 as dolomitic limestone. No systematic lateral variation was noted, but the upper part of the member tends to be slightly more calcitic than the lower part. Carbonate rock in the lower cherty member is generally medium gray and weathers to light olive gray. In general, it is rather thickly and obscurely bedded, but some beds are thin and parallel (stratigraphic section 1, pl. 3). In texture the carbonate rock ranges from fine crystalline to medium crystalline. Most samples are rather homogeneous in texture, but some show medium-crystalline calcite in a much finer dolomite matrix. Vuggy porosity is common but not universal.
Contact of the San Andres with the underlying Yeso Formation is conformable. Along the northern part of Algerita Escarpment it is easily recognized at the top of the highest siltstone bed of the Yeso. To the south the siltstone bed is absent, and the contact between the two formations is arbitrarily placed between relatively thin bedded noncherty slope-forming gray dolomite of the Yeso and the thicker bedded cherty more resistant light olive-gray-weathering dolomite of the San Andres.
Contact between the lower cherty member and the upper member of the San Andres is apparently conformable in the northwestern part of the area. In much of the area, chert is particularly abundant near the top of the lower member and virtually absent in the upper member, making the contact sharp; but in some places the amount of chert gradually decreases upward so that the contact is not so sharply defined.
For purposes of description the upper member of the San Andres Limestone in exposures north and west of the Last Chance Canyon drainage is divided into two approximately equal parts. The lower part consists of deeply pitted fine-crystalline light olive-gray to pale yellowish-brown dolomite and dolomitic limestone in beds 1 to 5 feet thick. It is typified by abundant recrystallized fusulinids and fusulinid molds. Calcite dolomite ratios computed from 1 spectrographic analysis reported by Boyd (1958, p. 24) and from 3 versenate analyses range from 75:25 to 9:91 and average 32:68. The upper part of the upper member is composed of laminated microcrystalline yellowish-gray to light olive-gray dolomite in beds 2 inches to 3 feet thick and of 1 to 3 thin units of fine-grained yellowish-brown sandstone. The slight compositional, textural, and color change between the two parts of the upper member is transitional and vaguely defined. Boyd (1955, p. 50; 1958, p. 22) apparently used this change as the contact between the San Andres and the overlying Grayburg Formation, but for reasons mentioned below (p. 29), the upper dolomite is here included with the San Andres (Hayes, 1959, p. 2210-2211).
The thickness of the San Andres Limestone is difficult to determine. The only place where the base and top of the formation are exposed within a reasonable horizontal distance is on Algerita Escarpment in sec. 3, T. 24 S., R. 20 E., where several high-angle strike faults are present. Stratigraphic section 1 (pl. 3) is a composite of partial sections measured in the fault blocks. In this composite section the San Andres is a little more than 1,200 feet thick, and in the Magnolia State "W" 1 well (sec. 16, T. 21 S., R. 22 E.) it is apparently 1,300 feet thick (pl. 2).
The San Andres Limestone in Last Chance Canyon and vicinity and in its southernmost exposures in the Dog Canyon area differs in several respects from the formation to the north. Local unconformities separate the upper and lower members of the San Andres, and the San Andres from the overlying Grayburg Formation. The lower cherty member changes somewhat in lithology southeastward as it approaches the basin-margin area, and the upper member largely completes its transition into the marginal facies.
The lower cherty member in Last Chance Canyon and vicinity is similar in overall appearance to equivalent rocks farther northwest, but it is more irregularly bedded and locally contains several thin layers of thinly bedded grayish-orange-weathering siltstone and silty claystone. Between the mouths of Roberts and Sitting Bull Canyons the beds pinch and swell, and several local angular unconformities and other irregularities are present in the bedding, which suggest deposition in an unstable area (fig. 13). Carbonate rock in the lower cherty member of the Last Chance Canyon area tends to be somewhat more calcitic, finer textured, and siltier than it is to the northwest. As calculated from versenate analyses of 13 samples from sections measured in Last Chance Canyon, calcite-dolomite ratios range from 3:97 to 96:4 and average 38:62; 6 samples are classed as dolomite, 2 as calcareous dolomite, 3 as dolomitic limestone, and 2 as limestone. Insoluble residues, consisting primarily of quartz silt, average from 10 to 15 percent in Last Chance Canyon and less than 5 percent to the northwest. The siltier carbonates tend to be yellowish gray rather than medium gray.
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| FIGURE 13.—Bedding features in the lower cherty member of the San Andres Limestone in Last Chance Canyon between tho mouths of Wilson and White Oaks Canyons. |
Thickness of the lower cherty member in Last Chance Canyon is unknown because the base is not exposed. A maximum of about 400 feet is exposed upstream from the mouth of Roberts Canyon. About 150 feet of beds at the top of the member in Roberts Canyon (stratigraphic section 7, pl. 3) is apparently missing near the mouth of Sitting Bull Canyon owing to erosion beneath the unconformity at the top of the member (stratigraphic section 9, pl. 3; fig. 14). Because of the unconformity, the lower cherty member in Last Chance Canyon is probably thinner than it is to the northwest. The thickness of the lower cherty member is unknown in the nearby Humble Huapache 1 or the Union White 1 wells because of thick intervals in which samples were not recovered. In the first-named well, however, the member is apparently at least 470 feet thick.
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| FIGURE 14.—Diagram showing stratigraphic relations in Last Chance Canyon between the mouths of Roberts (northwest) and Sitting Bull (southeast) Canyons. Grayburg Formation, Pg; upper member of San Andres Limestone, Psau; tongue of San Andres, Psat; sandstone tongue of Cherry Canyon Formation, Pcc; lower cherty member of San Andres Limestone, Psal. |
In the Last Chance Canyon area the upper member of the San Andres Limestone is thin. Near the mouth of Roberts Canyon it is 78 feet thick and consists of well bedded light-gray noncherty dolomite which contains abundant fusulinid molds in some beds (stratigraphic section 7, pl. 3). The member is similar throughout the Last Chance Canyon area, and its thickness ranges from about 50 to 100 feet. Five samples of carbonate analyzed by the versenate method proved to be dolomite with calcite-dolomite ratios of 2:98 to 5:95.
Between the mouths of Roberts and Sitting Bull Canyons the upper member of the San Andres thickens, and most of it grades laterally into the sandstone tongue of the Cherry Canyon Formation. The thickening is due to the appearance of progressively younger rocks beneath the pre-Grayburg unconformity at the top of the formation (pl. 3; figs. 14, 15).
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| FIGURE 15.—North wall of Wilson Canyon near locality of stratigraphic section 8. Thickening of the upper part of the lower cherty member of the San Andres Limestone (Psal) at left, thinning of the lowest tongue of the Cherry Canyon Formation (Pcc) at left, unusual swelling of a tongue of upper member of the San Andres Limestone (Psau) in center, transition of the upper member of the San Andres into the sandstone tongue of the Cherry Canyon Formation at right, and truncation of a tongue of the San Andres (Psat) and beds of the Cherry Canyon beneath evenly bedded Grayburg Formation (Pg). |
Most of the gradation between the upper member of the San Andres Limestone and the sandstone tongue of the Cherry Canyon Formation occurs between Wilson and Sitting Bull Canyons. A dolomite bed overlies, and interfingers with, the sandstone tongue of the Cherry Canyon and extends eastward at least as far as the NW1/4 sec. 35, T. 23 S., R. 22 E., where it plunges beneath the floor of Last Chance Canyon. The bed is probably a tongue of the San Andres, although it is truncated by the pre-Grayburg unconformity west of Sitting Bull Canyon and cannot be traced into the main body of the San Andres.
Near the mouth of Wilson Canyon, dolomite tongues of the San Andres Limestone extend eastward as far as half a mile into the Cherry Canyon Formation and then end abruptly by gradation into sandstone. These dolomite tongues are separated by sandstone tongues that pinch out westward into the San Andres. The eastward ends of the smaller tongues of dolomite and the basal few feet of the larger uppermost tongue of dolomite contain chert nodules similar to those in the sandstone tongue of the Cherry Canyon. The nodules diminish westward away from the sandstone tongue of the Cherry Canyon, and in Roberts Canyon no chert nodules occur in the upper member of the San Andres (stratigraphic sections 7 and 8, pl. 3; fig. 14).
The San Andres Limestone is overlain by the Grayburg Formation. Locally, the contact is an unconformity which is well displayed on the north walls of Last Chance and Wilson Canyons (figs. 14, 15) where more than 100 feet of uppermost beds of the San Andres are truncated in a distance of about a mile. The angular discordance here is about 1.5°. Unconformable relations between the two formations were not seen north or west of the Last Chance Canyon drainage in the Guadalupe Mountain area, but 20 miles to the southwest in the Brokeoff Mountains an unconformity is present above part of the transition zone between the upper member of the San Andres Limestone and the sandstone tongue of the Cherry Canyon Formation (Hayes, 1959, p. 2205-2206). This suggests that the unconformity is restricted to a narrow zone parallel to that facies boundary (fig. 9).
Where the contact between the San Andres and Grayburg is conformable, it is placed at the base of the lowest sandstone or siltstone bed in the Grayburg. Except near its transition into the sandstone tongue of the Cherry Canyon Formation, the San Andres is virtually free of clastic beds, whereas sandstone makes up one-third or more of the basal 75 feet of Grayburg.
The San Andres Limestone exposed in the area northwest of the Rocky Arroyo-Last Chance Canyon drainage divide is very sparsely fossiliferous, although fusulinid molds and dolomitized fusulinids are abundant in some layers, especially in the upper member. The transitional facies of the San Andres in Last Chance Canyon is, in general, more fossiliferous, and a few beds contain abundant silicified fossils. Newell and others (1953, p. 227-232) tabulated all fossil forms that had been previously described from the San Andres Limestone. Boyd (1958, p. 83-84) listed fossils from the northern exposures of the San Andres separately from those found in the transition facies and showed many forms which were previously undescribed from the San Andres. During the present investigation no additional forms were found in the upper member, but several previously unreported species of fusulinids were found in the lower cherty member in Last Chance Canyon. These fusulinids, which were identified by L. G. Henbest, of the Geological Survey (written communication, Apr. 11, 1958), have already been reported (Hayes, 1959, p. 2204) and include Parafusulina bosei var. attenuata (f—12396), Parafusulina sp. aff. P. sellardsi Dunbar and Skinner, 1937 (f—12398), and Parafusulina sp. cfr. "Schwagerina" setum Dunbar and Skinner, 1937 (f—12398).
Several geologists have collected fusulinids from the San Andres Limestone in Last Chance Canyon and Algerita Escarpment and have suggested age assignments for the rocks, but specific identifications have not been reported for most of the fusulinids. In summarizing age statements made by Skinner (1946, p. 1865), Wilde (1955, p. 59), Hollingsworth and Williams (in letter cited by Warren, 1955, p. 11), Clifton (1945, p. 1775), and Henbest (cited by Hayes, 1959, p. 2204), a latest Leonard and (or) earliest Guadalupe age was previously assigned to the lower cherty member in Last Chance Canyon (Hayes, 1959, p. 2202). Fusulinids collected by Clifton (1945, p. 1772-1773) and during the present investigation (Hayes, 1959, p. 2206) indicate a Guadalupe age for the upper member in Last Chance Canyon. This is to be expected in view of the laterally transitional relations of the upper member of the San Andres with the sandstone tongue of the Cherry Canyon Formation. Skinner (1946, p. 1865) collected several species of a fusulinid assemblage characterized by Parafusulina rothi from the lower cherty member on Algerita Escarpment (near stratigraphic section 1, pl. 3). This assemblage indicates equivalence to the Brushy Canyon or Cherry Canyon Formations. Skinner did not state from which part of the unit his fusulinids were collected, but they probably came from the upper 193 feet of the member which contains several fusulinid-bearing beds.
The distribution of exposures of the San Andres Limestone and equivalent rocks prevents direct field observation of the relations of the San Andres to rocks of the Delaware basin and the basin-margin area. Interpretation of those relations is summarized below following an enumerated review of the facts and assumptions which form the basis for the interpretations.
1. As stated above, beds in the upper part of the San Andres Limestone grade laterally into the sandstone tongue of the Cherry Canyon Formation.
2. Boyd (1955, p. 49; 1958, p. 14) demonstrated that beds in the lower part of the San Andres grade laterally into the Cutoff Shale.
3. The age and correlation of the Cutoff is somewhat controversial, but Newell and others (1953, fig. 7) consider it to be equivalent to the upper part of the Bone Spring Formation of the Delaware basin, and this correlation is tentatively accepted here.
4. P. B. King (1948, p. 20, 30) worked out relations in the Texas part of the Guadalupes that indicate that the contact between the Cutoff and the sandstone tongue of the Cherry Canyon Formation is an unconformity representing Brushy Canyon time.
5. As noted above, fusulinids collected by Skinner (1946, p. 1865) indicate a Guadalupe age for at least the upper 193 feet of the lower cherty member of the San Andres Limestone on Algerita Escarpment.
6. No unconformity is evident within or at the base of the lower cherty member in that area.
7. There is also no indication of an unconformity at the top of the San Andres in the northwestern part of the area, but in Last Chance Canyon the upper most beds equivalent to the sandstone tongue of the Cherry Canyon Formation are missing beneath a local pre-Grayburg unconformity.
8. The basal beds of the Grayburg Formation are traceable from Last Chance Canyon to Algerita Escarpment and apparently are, virtually synchronous across that interval.
9. The entire Grayburg Formation is apparently laterally transitional into the lower part of the Goat Seep Dolomite.
10. Total combined thickness of the Cutoff Shale and sandstone tongue of the Cherry Canyon Formation is less than 600 feet (King, P. B., 1948, pl. 6), whereas the San Andres Limestone is more than 1,200 feet thick.
Items 2, 3, and 5 listed above indicate that the lower 340 feet or less of the lower cherty member of the San Andres Limestone is laterally transitional southeastward into the Cutoff Shale of the basin-margin area. It is possible, however, that the lowermost beds of the San Andres are equivalent to the uppermost part of the Victorio Peak Limestone. Items 1, 7, 8, 9, and 10 above indicate that the upper part of the upper member of the San Andres of northwestern exposures is transitional into the sandstone tongue of the Cherry Canyon Formation, except where removed by pre-Grayburg erosion. It is possible, but considered doubtful, that the uppermost beds of the San Andres were once transitional into the lowest beds of the Goat Seep Dolomite, as inferred by Newell and others (1953, fig. 6).
The correlations stated above and item 6 indicate that rocks about 580 feet thick comprising the lower part of the upper member and the upper part of the lower cherty member of the San Andres Limestone in the northwestern part of the mapped area probably are equivalent to the Brushy Canyon Formation of the Delaware basin. This middle part of the San Andres, however, probably was never coextensive with the Brushy Canyon. P. B. King (1948, p. 30) has demonstrated that the Brushy Canyon Formation overlaps black limestone of the Bone Spring Limestone and the Cutoff Shale on the Bone Spring monocline. Thus, that flexure apparently forms the southeast flank of an arch, 15 to 20 miles wide, which was overlapped on the northwest by the middle part of the San Andres Limestone.
ARTESIA GROUP
The Artesia Group was named by Tait and others (1962, p. 511) to include, in ascending order, the Grayburg, Queen, Seven Rivers, Yates, and Tansill Formations. As defined, the group includes a carbonate facies adjacent to the basin-margin facies and an evaporite facies farther shelfward. The Artesia Group thus replaces the abandoned Carlsbad Group which was defined to include the carbonate facies only of the Seven Rivers, Yates, and Tansill Formations (Hayes, 1957). Inasmuch as the constituent formations of the Artesia Group are distinguishable within the evaporite facies in the subsurface throughout southeastern New Mexico (Tait and others, 1962, p. 514-515), the Chalk Bluff Formation of Lang (1937, p. 855-857) is also abandoned. The Chalk Bluff originally included all the rocks in the evaporite facies from the top of the San Andres Limestone to the base of the Salado Formation.
GRAYBURG FORMATION
The rocks here included in the Grayburg Formation have been assigned in the past to many stratigraphic units. Exposures of the Grayburg in the northern part of the area were apparently included by Baker (1920, p. 117) in the base of the †Pecos Valley Red Beds of Beede (1910, p. 131). Darton and Reeside (1926, fig. 3—A), and later Crandall (1929, p. 933-935), included the Grayburg in the upper part of the †Chupadera Formation. Lloyd (1929, p. 653) apparently included the Grayburg at the base of his Red sand group, where as Blanchard and Davis (1929, pl. 10) mapped it as the upper part of the San Andres Limestone. Fiedler and Nye (1933, pl. 9—B) included the Grayburg in the base of their Pecos Formation in the area just north of the present report area. The Dog Canyon Limestone of Lang (1937, p. 858-859) probably was approximately synonymous with the present-day Grayburg Formation and Goat Seep Dolomite. P. B. King (1948, p. 40), who abandoned the term Dog Canyon in favor of Goat Seep, used the latter term to include rocks located to the north that are now assigned to the Grayburg and Queen Formations. Skinner (1946, p. 1865-1867) included the Grayburg in the lower part of the Queen Formation.
The term Grayburg was proposed by Dickey (1940, p. 44-45) who designated the Cecil H. Lockhart Root Permit 2 in sec. 7, T. 17 S., R. 30 E., Eddy County, N. Mex., as the subsurface type locality and suggested that at some future time the unit should be measured and defined on the outcrop in the Guadalupe Mountains. The earliest known use of the term for rocks cropping out in the Guadalupe Mountains is in a mimeographed guidebook (Stipp, 1951). Newell and others (1953, p. 43) used the term Grayburg Formation provisionally in the Guadalupe Mountains. Moran (1954) proposed locations for surface type sections of the Grayburg and Queen Formations in the Guadalupes, but he did not present either written or graphic sections. However, the use of the term Grayburg in this report and earlier reports (Hayes and Koogle, 1958; Hayes, 1959, p. 2207-2209) probably conforms closely to that intended by Moran. Boyd (1958, p. 28) mapped the unit with the Queen Formation referring to the combination as the "Grayburg-Queen sequence" in the El Paso Gap quadrangle because of the difficulty of distinction between the two formations in the many fault blocks of that quadrangle.
The Grayburg Formation crops out in a band several miles wide, extending from Martine Ridge northeastward across the mapped area. There are also inliers to the southeast and outliers to the northwest.
The Grayburg Formation overlies the San Andres Limestone and underlies the Queen Formation. It grades laterally southeastward into the lower part of the Goat Seep Dolomite.
Like most of the formations of the shelf facies, the Grayburg changes in character from southeast to northwest, but the following general description applies to most exposures in the report area. About four-fifths of the formation is very pale orange (weathering to grayish-orange) compact very finely textured dolomite and calcareous dolomite that generally occurs in beds 1 inch to 1 foot thick, although some beds are as thick as 10 feet. The rest of the formation consists of similarly colored very fine grained calcareous or dolomitic quartz sandstone mostly in beds 1 to 6 inches thick and in a few beds as thick as 5 feet. The proportion of sandstone to dolomite is somewhat greater in the lower part of the formation where some sandstone beds are locally very resistant (stratigraphic sections 9 and 10, pl. 3; fig. 15). Calcite-dolomite ratios of carbonate rock from the Grayburg computed from 8 spectrographic analyses (Boyd, 1958, p. 31) and from 5 versenate analyses made for this report range from 17:83 to 0:100 and average 4:96. Of the samples analyzed, 11 are classed as dolomite and 2 as calcareous dolomite.
The Grayburg in Gilson and Trimble Canyons is about 435 feet thick (stratigraphic sections 10 and 11, pl. 3), and it is 425 feet thick on the Shattuck Valley scarp (stratigraphic sections 18 and 19, pl. 3). A section of the Grayburg reported by Moran (1954) as 475 feet thick in Sitting Bull and Gilson Canyons may include 50 feet of dolomite at the base that is here mapped as a tongue of the San Andres Limestone (pl. 1). The Grayburg thickens southeastward and may be as thick as 600 feet near its transition into the Goat Seep Dolomite. Conversely, it probably thins to 400 feet or less near the north edge of the area. In the subsurface of northeastern Eddy and Lea Counties the Grayburg ranges in thickness from about 200 to 450 feet and averages about 325 feet (Bates, 1942b).
The contact between the Grayburg Formation and the underlying San Andres Limestone appears parallel and conformable throughout the area, except for the local low-angle unconformity in the Last Chance Canyon area described on page 27. Everywhere the contact is marked by a rather sharp change in lithology. Almost sandstone-free yellowish-gray to light olive-gray-weathering dolomite in the upper part of the San Andres contrasts with the alternating beds of grayish-orange-weathering sandstone and dolomite in the lower part of the Grayburg (pl. 3). In the El Paso Gap quadrangle the basal contact of the Grayburg Formation as designated by Boyd (1958, p. 22) is about 300 feet lower than the contact used in this report. The contact used here is preferred because it is more easily mapped, and because it agrees more closely with Dickey's (1940, p. 44-47) original definition. Reasons for placing the contact as used in this report have previously been reported in detail (Hayes, 1959, p. 2210-2211).
The contact between the Grayburg Formation and overlying Queen Formation is arbitrarily placed at the base of a locally conspicuous sandstone sequence assigned to the Queen.
The lateral transition of the Grayburg Formation into the Goat Seep Dolomite is partly exposed in the report area in the upper end of North McKittrick Canyon (pls. 1, 3). The complete transition can be seen below Blue Ridge on the west side of the Guadalupe Mountains in Texas, 5 miles south of the present mapped area (Newell and others, 1953, p. 45). Graphic sections illustrating the transition at that locality are shown by P. B. King (1948, stratigraphic sections 5 and 6, pl. 6). Near the transition into the Goat Seep Dolomite, dolomite of the Grayburg changes from very pale orange to light gray, and becomes coarser and thick bedded; the sandstones become increasingly dolomitic and grade into slightly sandy dolomite. Fusulinid molds and oolitic layers are common in the dolomite beds of the Grayburg in the transition zone (fig. 16). Most of the Grayburg Formation exposed in Dark and Trimble Canyons is in the transition zone.
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| FIGURE 16.—Photomicrograph of dolomite from near the top of the Grayburg Formation at stratigraphic section 20. This oolitic dolomite is typical of the Grayburg and Queen Formations near their transition into the Goat Seep Dolomite. Oolites are in a finely crystalline dolomite matrix. Large dark area in center is a rounded clast of sandy dolomite possibly derived from the Goat Seep. 1 mm-long arrow points up. |
Near the north edge of the mapped area, dolomite of the Grayburg is very thin bedded, aphanitic gypsum beds are present, and sandstone beds are less resistant and pinker than in areas farther to the south. In the vicinity of Box Canyon the basal 50 feet of the formation is about 30 percent friable yellowish-gray sandstone, 30 percent friable pale-red sandstone and siltstone, 30 percent thin-bedded aphanitic dolomite, and 10 percent gypsum. Within a distance of 5 miles north of the mapped area, virtually all the sandstone is replaced by red beds and much of the dolomite by gypsum.
Although the term Grayburg was applied to rocks in the Guadalupe Mountains as early as 1951 (Stipp, 1951; 1952, p. 8-10; Newell and others, 1953, p. 43; Moran, 1954; Boyd, 1958, p. 28), there was doubt as to the actual equivalence of the rocks so identified with the original subsurface Grayburg Formation. In an earlier paper (Hayes, 1959, p. 2208), evidence was presented to show that the surface and subsurface Grayburg are virtually the same. The Grayburg Formation can easily be correlated in a series of wells from its subsurface type in Lockhart Root Permit 2 well in eastern Eddy County to Magnolia State "W" 1; the latter well was located on outcrops of the Grayburg in the report area (fig. 17).
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| FIGURE 17.—Surface and well sections showing correlation of the Grayburg and Queen Formations from outcrop area in Guadalupe Mountains to original subsurface type section of the Grayburg Formation in Lockhart Root Permit 2 well (Dickey, 1940). Well sections were interpreted from sample descriptions. Numbers to left of well sections indicate depth in feet below surface; numbers to left of composite surface section indicate stratigraphic interval above base of the Grayburg Formation. |
QUEEN FORMATION
The Queen Formation was originally named the Queen Sand by Crandall (1929, p. 940) for exposures in the vicinity of the old Queen Post Office, sec. 30, T. 24 S., R. 22 E., but a type section was not designated. Only the lower part of the formation is exposed near the ruins of Queen, but the upper part of the unit was identified by Crandall (1929, p. 940) in Rocky Arroyo, T. 21 S., R. 24 E. The Queen was subsequently recognized in many oil fields in the shelf areas of southeast New Mexico (Bates, 1942b). The upper and lower limits of the formation on the surface were formally defined by Newell and others (1953, p. 44-45). Moran (1954) established a type locality for the formation on the west wall of Dark Canyon in SW1/4 sec. 36, T. 24 S., R. 22 E.
In the mapped area the Queen Formation is exposed in an irregularly shaped northeastward-trending outcrop band extending from Shattuck Valley to the northwest side of the Hess Hills. It is also exposed in Fawn Valley, Johnson and Trail Canyons, and in many small outliers on the Grayburg Formation.
The Queen Formation is lithologically similar to the Grayburg Formation; the two units differ primarily in the proportion of contained rock types. An average of about one-fifth, and at no place more than one-fourth, of the Grayburg consists of clastic rocks; an average of two-fifths, and at no place less than one-third, of the Queen is made up of clastic rocks.
Carbonate rock of the Queen and Grayburg are similar. In general, it is very pale orange compact very finely textured dolomite and calcareous dolomite that weathers pale yellowish brown. Individual beds are generally less than 1 foot thick, though some beds are as much as 5 feet thick. Calcite-dolomite ratios computed from spectrographic analyses of 4 samples (Boyd, 1958, p. 31) and from versenate analyses of 9 samples made during the present work range from 48:52 to 0:100, and average 10:90. Of the samples analyzed, 9 are classified as dolomite and 4 as calcareous dolomite.
Clastic rocks in the Queen are largely confined to the upper 100 feet and the lower 50 feet of the formation. The clastic rocks consist of very pale orange very fine grained sandstone and siltstone that weathers pale yellowish brown and is cemented with carbonate. Sandstone is predominant in the lower part of the formation, and siltstone is predominant in the upper part. In general, the sandstone occurs in beds more than a foot thick, whereas the siltstone is generally in thin platy beds. The largely silty sequence in the top 100 feet of the Queen Formation was named the Shattuck Member by Newell and others (1953, p. 45) for outcrops along the Shattuck Valley escarpment in the vicinity of Devils Den. The member was not mapped separately during the present investigation.
The thickness of the Queen Formation ranges from about 210 feet below Deer Hill on the Shattuck Valley escarpment (stratigraphic section 19, pl. 3) to a reported 421 feet at Moran's (1954) type section in Dark Canyon. It is 378 feet thick at the site of an abandoned CCC camp farther down Dark Canyon (stratigraphic section 12, pl. 3, and p. 59-60). Bates (1942b) reports subsurface thicknesses of the Queen ranging from 305 to 475 feet and averaging about 400 feet in oil fields in northeastern Eddy and Lea Counties.
The contact between the Queen Formation and underlying Grayburg Formation is conformable and is arbitrarily placed at the base of a locally conspicuous sandstone bed (stratigraphic sections 11, 12, 19, 20, pl. 3). This basal sandstone varies in thickness and is difficult to trace at some places. It is particularly difficult to identify in isolated outcrops and where exposures are poor. Boyd (1958, pl. 1) mapped the Queen and Grayburg as a single unit which he called the "Grayburg-Queen" sequence. Skinner (1946, p. 1865-67) included both the Queen and Grayburg of this report in his Queen Formation, but recognized the probable equivalence of the lower part to the Grayburg of the subsurface.
The contact between the Queen Formation and overlying Seven Rivers Formation is sharp, but it is parallel and apparently conformable. The siltstone of the Shattuck Member at the top of the Queen is easily distinguished from the dolomite or gypsum beds at the base of the Seven Rivers.
Most of the Queen Formation grades laterally southeastward into the upper part of the Goat Seep Dolomite, but the upper part of the Shattuck Member may pinch out between the Goat Seep and overlying Capitan Limestone (fig. 9). Rocks transitional from the Queen to Goat Seep are exposed in the walls of North McKittrick Canyon (stratigraphic sections 20 and 21, pl. 3). The transitional beds are very similar to the already-described underlying rocks that are transitional from the Grayburg to Goat Seep. As is true in most of the other facies changes in the report area, the Grayburg and Queen grade into the Goat Seep farther to the southeast in the younger beds, so that the Queen Formation locally overlies part of the Goat Seep (pls. 1, 3).
The lithology of the Queen Formation changes toward the northwest, although this cannot be seen in the mapped area because so little of the Queen is preserved in outcrops. Within the Seven Rivers Embayment (fig. 1), however, the dolomite of the Queen is largely replaced by gypsum, and the clastic beds of the formation change from very pale orange to pale reddish brown. These changes occur in the subsurface and are illustrated in figure 17.
The Queen of subsurface usage, as identified by Dickey (1940, p. 45) in the Lockhart Root permit 2 well in northeastern Eddy County (stratigraphic section 7, T. 17 S., R. 30 E.) can be correlated in a series of wells from the Lockhart well to the Kinkaid and Watson Stanolind-Federal 1 (sec. 3, T. 20 S., R. 25 E.) (fig. 17); the latter was drilled on the outcrop of the Queen Formation (Dane and Bachman, 1958). The Shattuck Member at the top of the Queen is probably the "Artesia red sand" of subsurface usage (Bates, 1942b).
SEVEN RIVERS FORMATION
The term Seven Rivers was first applied by Meinzer, Renick, and Bryan (1926, p. 13-14) to the Seven Rivers Gypsiferous Member of the now-abandoned Chupadera Formation for exposures south of Seven Rivers, at the north end of the Seven Rivers Hills (fig. 1). Lang (1937, p. 860) included the Seven Rivers Gypsiferous Member in his Chalk Bluff Formation, but he recognized the contemporaneity of the Seven Rivers and the lower part of his Carlsbad Formation. As the result of a symposium (DeFord and Lloyd, 1940, p. 8-11), the Seven Rivers was raised to formational status and expanded laterally to include equivalent bedded carbonates.
The Seven Rivers Formation conformably overlies the Queen Formation, conformably underlies the Yates Formation, and grades laterally southeastward into the lower part of the Capitan Limestone. It is exposed in continuous outcrop from North McKittrick Canyon to the East Hess Hills and in many inliers and outliers.
The bedded carbonate facies of the Seven Rivers between its southeastward transition into the Capitan Limestone and its northwestward transition into the evaporite facies is 5 to 7 miles wide. Lateral changes in lithology and bedding within the carbonate facies are considerable, but, in general, the unit consists dominantly of yellowish-gray dolomite which weathers light olive gray. Also present, but constituting less than 10 percent of the formation, are a few beds of very pale orange quartzose siltstone cemented with dolomite. Calcite-dolomite ratios of the carbonate rock were computed from versenate analyses of 8 samples collected during the present work, from chemical analyses of 2 samples reported by P. B. King (1948, p. 66), and from 1 spectrographic analysis reported by Newell and others (1953, p. 61). These ratios range from 32:68 to 0:100 and average 6:94. Nine of the samples are classed as dolomite, and two, both collected from near the transition into the Capitan Limestone, are classed as calcareous dolomite.
Individual beds of dolomite in the Seven Rivers range in thickness from 5 to 10 feet or more near the Capitan Limestone and are generally less than 1 foot thick near the transition into the evaporite facies. The texture of the dolomite also changes markedly. Adjacent to the Capitan Limestone, fusulinid coquinas are common (fig. 18) and dolomitized mollusks occur. Farther northwestward, from a few hundred feet to 2 miles from the Capitan, pisolites generally less than 1 inch in diameter are extremely abundant and locally make up much of the formation (stratigraphic section 14, pl. 3). The pisolites become smaller to the northwest, and the pisolitic facies is bounded on the northwest by a narrow oolitic facies (fig. 19). Still farther northwestward, the dolomite of the Seven Rivers is increasingly fine grained, and near its transition zone to the evaporite facies it is aphanitic.
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| FIGURE 18.—Photomicrograph of fusulinid coquina from the Seven Rivers Formation near its transition into the Capitan Limestone. Fusulinids (probably Polydiexodina) are all oriented in same direction with long axes subparallel to trend of facies change. Smaller circular bodies randomly mixed with the fusulinids are the algae Mizzia. Matrix is very finely crystalline dolomite partially replaced by sparry calcite. 1 mm-long arrow points up. |
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| FIGURE 19.—Photomicrograph of pisolitic carbonate from the lower part of the Seven Rivers Formation at stratigraphic section 21. Large pisolite has a nucleus of three smaller pisolites which, in turn, have nucleae of several oolites and minute rock fragments. White areas are crystalline calcite which has apparently replaced the outer edges of the pisolites and some of the dolomite matrix. Bar is 1 mm long. |
Unusual sedimentary features, called tepee structures by Adams and Frenzel (1950, p. 305), are common in dolomite of the Seven Rivers within 2 miles of the Capitan Limestone. These structures, which are more conspicuous in the overlying Yates Formation, are described on pages 34-35.
The transition of individual beds of the Seven Rivers into the Capitan takes place within a few hundred feet but, from the base to the top of the Seven Rivers, the transitional zone shifts southeastward more than 1 mile (pls. 1, 3). In approaching the Capitan, carbonate beds of the Seven Rivers first thicken conspicuously and then the bedding planes disappear in the virtually unbedded Capitan Limestone. The dolomite of the Seven Rivers simultaneously changes rather abruptly into the almost pure limestone of the Capitan. The changes in bedding and mineralogy are accompanied by changes in texture from bioclastic and pisolitic in the Seven Rivers to biogenic in the Capitan. Accompanying the change in the carbonate rocks, the thin siltstone beds of the Seven Rivers become increasingly dolomitic and then either abruptly grade into limestone or pinch out.
The lateral gradation within the Seven Rivers formation from the carbonate to the evaporite facies takes place near the northwest limit of exposures of the Seven Rivers Formation in the mapped area. The geologic map (pl. 1; see also fig. 9) shows the approximate position of the facies change on the southeast side of the Hess Hills. The change also occurs near El Paso Gap where an outlier of Seven Rivers in Shattuck Valley is evaporite rock, whereas a short distance to the south on El Paso Ridge, the Seven Rivers consists mostly of carbonate rocks. Boyd (1958, p. 16-17 and pl. 1) mapped these rocks near El Paso Gap as a part of the Grayburg Formation.
The change from the carbonate facies to the evaporite facies takes place within a few hundred feet laterally. Rocks in the transition zone are not well exposed, in the mapped area, but they can be seen on the north side of Last Chance Canyon above the mouth of Johnson Canyon, about 2 miles north of the mapped area. The transitional rocks are well exposed also in Rocky Arroyo at the south edge of the Seven Rivers Hills (fig. 1). Bates (1942a) described the facies change at that locality, where it is accomplished by interfingering of thin beds of dolomite and gypsum as well as by abrupt southeastward lithologic change from gypsum to carbonate rock. Some thin beds of sublithographic dolomite extend far into the evaporite facies. A tongue of dolomite that extends northwestward over the gypsiferous lower part of the formation was named the Azotea Tongue by Lang (1937, p. 868) for exposures on the west edge of Azotea Mesa (fig. 1). The siltstone beds of the Seven Rivers change from very pale orange in the main body of the carbonate facies to pale reddish brown near the zone transitional with the evaporite facies. Although it is not evident within the mapped area, the gradation takes place progressively farther northwestward from bottom to top of the Seven Rivers. In the subsurface, beneath the zone of surface hydration, sulfate rock of the evaporite facies is anhydrite rather than gypsum.
The Seven Rivers Formation is about 460 feet thick at Bear Canyon (stratigraphic section 13, pl. 3; p. 60-61), about 1-1/2 miles northwest of the Capitan Limestone, and is probably about the same thickness else where at the same distance from the Capitan. The formation thickens near the Capitan to a possible 600 feet.
YATES FORMATION
The Yates Sandstone was named by Gester and Hawley (1929, p. 487-488) as a subsurface unit in the Yates oil field, Pecos County, Tex. It was subsequently recognized as "the most persistent lithologically of all formation of Whitehorse age in the West Texas-New Mexico Permian basin" (Fritz and FitzGerald, 1940, p. 25) and "is one of the best known and most reliable widespread stratigraphic key horizons in the Permian basin" (Woods, 1940, p. 34). Woods (1940, fig. 1) and Dickey (1940, fig. 1) correlated the top of the Yates from Pecos County, Tex., into Lea and Eddy Counties, N. Mex. DeFord, Riggs, and Wills (1938) traced the Yates from the subsurface to outcrops near Carlsbad, and DeFord and Riggs (1941, fig. 3) published a line of stratigraphic sections showing correlation of the Yates and overlying Tansill Formation between the subsurface in Lea County and a surface section measured less than 2 miles from the present mapped area in and near the SW1/4 sec. 27, T. 23 S., R. 25 E. The Yates Formation of the surface, as established by DeFord and Riggs, is used in this report. The Three Twins Member of the Chalk Bluff Formation (Lang, 1937, p. 862-863) is virtually the same as the evaporite facies of the Yates and Tansill Formations combined. The name Three Twins is therefore abandoned.
In the mapped area, the Yates Formation crops out in many outliers and inliers on and near northeastward-trending Guadalupe Ridge. It is most extensively preserved in the northern part of the area.
The Yates is underlain by the Seven Rivers Formation and overlain by the Tansill Formation with conformable but sharp contacts (figs. 20, 26). As stated above, the Yates grades southeastward into the Capitan Limestone. The Yates is characterized by very persistent siltstone and sandstone beds which make up 1/3 to 2/3 of the formation; the adjacent Seven Rivers and Tansill Formations are predominantly dolomite.
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| FIGURE 20.—Contact between siltstone at the top of the Yates Formation and dolomite at the base of the Tansill Formation along Carlsbad Caverns National Park road in S1/2 sec. 30, T. 24 S., R. 25 E. |
As in the Seven Rivers Formation, lithology of the Yates is variable laterally in a southeast-northwest direction. Dolomite of the Yates is similar to that of the Seven Rivers. Near the transition into the Capitan the dolomite is very thick bedded and bioclastic and contains abundant fusulinids. Farther to the northwest the rock is thick bedded and pisolitic. Beyond the pisolitic facies is a narrow band in which the rock is oolitic. Still farther northwest the dolomite is more thinly bedded, and it becomes aphanitic as one approaches the zone in which dolomite is transitional into evaporites. Versenate analyses for calcium and magnesium were made of three samples of carbonate rock from the Yates. Computed calcite-dolomite ratios range from 12:88 to 0:100 and average 6:94. One sample is classified as calcareous dolomite and two as dolomite.
Many small primary structures resembling anticlines, called tepee structures by Adams and Frenzel (1950, p. 308), are present in the dolomite beds of the Yates within about 1-1/2 miles of the Capitan Limestone. Similar structures also occur in the Seven Rivers and Tansill Formations, but they are much more common in the Yates. Those in the Yates are particularly conspicuous in Walnut Canyon. They are confined to layers 3 to 30 feet thick which are overlain and underlain by undisturbed beds. The structures are seldom exposed except in cross section, but they are apparently linear and are always anticlinal. As noted by Newell and others (1953, p. 127-128), no systematic trend of the structures is apparent. The individual beds involved in the structures are commonly broken and crumpled along the axial planes, which commonly contain recrystallized dolomite. Most of the folds are confined to dolomite, but, in some, very thin beds of siltstone are involved. Most of the structures flatten abruptly upward, owing to thinning of dolomite beds over the crests; in a few, the crests of the folds are truncated. All are obviously primary structures.
Adams and Frenzel (1950, p. 307-308) attributed the folds to compression contemporaneous with deposition, but they said that the cause of the compression was not apparent. Newell and others (1953, p. 126-127), however, noted that the folds do not display such compressional features as overturned axial planes and shear surfaces. They postulated that gypsum may have "squeezed upward along joints, penetrating between the layers close to the joint and working its way upward until all the gypsum from what must have been a thin layer was exhausted," or that the structures "may have formed during the Permian period by expansion of crystallizing salts, perhaps the inversion of anhydrite to gypsum, along joints and bedding planes." A combination of the two processes postulated by Newell and others (1953, p. 126-127) would also seem reasonable, that is, that anhydrite was squeezed upward along joints and later inverted to gypsum, except that there is little evidence that sufficient anhydrite or gypsum was deposited so close to the Capitan Limestone during Yates time. Boyd (1958, p. 50-51) observed similar tepee structures in the "Grayburg-Queen sequence" and suggested that "Intrastratal flowage of material in unconsolidated beds due to differential loading merits equal consideration as a cause." It is here suggested that intrastratal flowage of unconsolidated sediment might have taken place down the slight depositional slope away from the Capitan Limestone. This would, of course, have induced minor compression and probably could have produced the tepee structures.
The quartzose siltstone and sandstone units in the Yates Formation are less resistant to erosion than is dolomite, and they generally weather to slopes between cliffs and ledges of dolomite. They are generally laminated and occur in beds which range in thickness from less than 1 inch to several feet. The color of the weathered rock is mostly very pale orange and grayish orange near the Capitan Limestone and is reddish orange and reddish brown farther northwest.
Detrital grains in the siltstone and sandstone are mostly quartz, but scattered feldspar grains are generally present (fig. 21). The average grain size is very close to the division between silt and very fine sand. Sandy siltstone probably is more abundant than silty sandstone, however. Size sorting is generally very good. Cementing material in the siltstone and sandstone is generally dolomite, but in some beds it is calcite cement. Argillaceous material makes up a very small fraction of all the clastic rocks and seems to increase toward the northwest. Within 2 miles of the Capitan, the siltstone and sandstone beds locally contain numerous nodules, as much as several inches in diameter, of limonite or goethite pseudomorphous after pyrite.
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| FIGURE 21.—Photomicrograph of well-sorted coarse siltstone from the Yates Formation. Cementing material is dolomite which has apparently replaced outer margins of quartz grains. Larger irregular light-gray areas are dolomite. Small opaque spherules may be limonite or pyrite. Bar is 1 mm long. |
Lateral transition of the Yates Formation into the Capitan Limestone takes place farther to the southeast than transition of the Seven Rivers into the Capitan, and the upper part of the Yates makes the transition farther to the southeast than does the lower part (pls. 1, 3; fig. 9). Rocks in the transitional zone are particularly well displayed on the north wall of Slaughter Canyon (fig. 10). Near the Capitan, dolomite beds of the Yates thicken conspicuously and become calcitic. At the vaguely defined boundary between the Yates and the Capitan, bedding planes disappear and the carbonate becomes limestone. At approximately the same place, sandstone and siltstone of the Yates grade rather abruptly into limestone (stratigraphic sections 2 to 6, pl. 3). Several hundred feet southeast of the Yates-Capitan boundary the stratigraphic horizon of the highest siltstone of the Yates is represented by a notch in the Capitan Limestone cliffs (stratigraphic sections 6 and 17, pl. 3). Newell and others (1953, p. 131-140) discussed in detail facies changes within dolomite of the Yates.
Transition of the dolomite facies of the Yates into the evaporite facies is not complete in the report area; however, the transition can be seen in poor exposures to the northeast near Carlsbad, and it is well known in the subsurface east of Carlsbad. In exposures of the Yates northwest of Crooked Creek the dolomite is very thin bedded and aphanitic, the siltstone is pale red, and the formation contains some gypsum. This lithology indicates that even though it is now removed by erosion, the evaporite facies was once present a short distance northwest of the present exposures.
The Yates Formation is 328 feet thick3 where measured in North Rattlesnake Canyon (stratigraphic section 2, pl. 3; p. 59). Toward its transition into the Capitan Limestone in North Slaughter Canyon the formation thickens to at least 375 feet, owing to a thickening of the dolomite beds (stratigraphic section 16, pl. 3). In two sections measured in Dark Canyon in T. 23 S., R. 25 E., a few miles outside the report area, the Yates is 262 and 287 feet thick.
3A previously reported thickness of 270 feet for the Yates in North Slaughter Canyon (Hayes and Koogle, 1958) is erroneous.
TANSILL FORMATION
The Tansill Formation is the youngest formation in the Artesia Group. Exposures about 4 miles northwest of Carlsbad, near the reservoir behind Tansill power dam, were first formally described as the Tansill by DeFord and Riggs (1941).
The Tansill Formation is extensively exposed northeast of Walnut Canyon; to the southwest it forms outliers capping the Reef Escarpment. The Tansill conformably overlies the Yates Formation and Yates equivalents in the massive member of the Capitan Limestone. The Tansill grades southeastward into the upper most part of the Capitan Limestone. No younger beds of Permian age overlie the Tansill Formation within the mapped area, but the Tansill is overlain by the Salado Formation in the subsurface east of the Pecos River (fig. 2). The upper contact has been discussed on page 16.
Within the report area, the Tansill Formation is composed mainly of dolomite which is nearly identical to the dolomite in the Seven Rivers and Yates Formations. It also contains thin beds of siltstone similar to siltstone in the two underlying formations. A siltstone unit 8 feet thick, called the Ocotillo Silt Member by DeFord and Riggs (1941, p. 1717), occurs about 100 feet above the base of the Tansill. This siltstone was not mapped, but it is traceable over much of the northern part of the Tansill outcrop area.
The transition of the Tansill into the Capitan Limestone takes place southeast of the Yates and Capitan transition, and the upper part of the Tansill grades into the Capitan southeast of the transition of the lower part of the Tansill into the Capitan. The facies change is virtually identical to the Seven Rivers and Capitan transition. In the subsurface northeast of Carlsbad, the Tansill grades laterally shelfward from carbonates to evaporites within a few miles of the Capitan, but in the report area rocks showing the carbonate-evaporite facies change were removed by erosion. Presumably, it is much like the carbonate-evaporite transition of the Seven Rivers described on page 33.
It is impossible to measure a complete thickness of the Tansill in the report area because its top is not preserved. DeFord and Riggs (1941, p. 1723) believed that about 5 feet of rock was missing from the top of the Tansill at the type locality, where they measured a thickness of 123.5 feet for the formation. They reported (p. 1722) that the Tansill thickens to more than 300 feet southeastward near the Capitan Limestone. An incomplete section about 325 feet thick is preserved in Rattlesnake Canyon (stratigraphic section 5, pl. 3) very near the Capitan. In the subsurface in Eddy and Lea Counties, the Tansill ranges between about 90 to 200 feet in thickness (Bates, 1942b).
FOSSILS OF THE ARTESIA GROUP
In the northern part of the area, the Grayburg and Queen Formations seem to be almost completely devoid of fossils, but toward the south dolomitized and silicified fossils and fusulinid molds occur sporadically. Boyd (1958, p. 67-71) reported on several collections from the "Grayburg-Queen sequence," but some were apparently from beds here included in the upper part of the San Andres Limestone. Concerning one definite Grayburg fossil locality in SW1/4SW1/4 sec. 9, T. 25 S., R. 21 E., Boyd (p. 70) states
"Composita and Hustedia were found associated with numerous gastropods, including one bellerophontid species, 2 subulitid species, and one naticopsid species, which were represented by more individuals than were all the other species combined."
His largest collection, from near Hamm Draw in sec. 2, T. 25 S., R. 21 E., is believed to have been from the uppermost part of the Grayburg Formation, although it was reported to be from the Queen. The collection contained representatives of at least 26 species of mollusks, 1 coral, 1 ostracode, and bryozoan fragments (Boyd, 1958, p. 85-86). The gastropod Bellerophon majusculus was most abundant. Newell and others (1953, p. 143) collected specimens from the Grayburg at six localities and reported Parafusulina, crinoids, brachiopods, pelecypods, gastropods, nautiloids, and algae; but their faunal list (p. 227-232) does not identify species. Locality 7628 reported by Girty (in P. B. King, 1948, p. 48-49) is almost certainly in the Grayburg, but in the report the fossils collected there were not separated from those collected in the Goat Seep Dolomite and Queen Formation. Needham (1937, p. 56-58) described the fusulinid Parafusulina dunbari which was found near the middle of the Dog Canyon Limestone (of former usage, Grayburg Formation of this report) along Last Chance Canyon. According to Lloyd G. Henbest (written communication, Apr. 14, 1958), "this species * * * seems to be synonymous with Parafusulina rothi Dunbar and Skinner, 1936" (Dunbar and others, 1935). No fossils were collected from the Grayburg during the present investigation.
Newell and others (1953, p. 41-42) identified the fusulinids Parafusulina maleyi and Rauserella erratica found in the upper part of the Queen Formation in sec. 32, T. 24 S., R. 23 E., near the abandoned CCC camp in Dark Canyon (stratigraphic section 12, pl. 3). Although not identified as to species on their faunal chart (p. 227-232), they also reported (p. 143) crinoids, echinoids, bryozoans, pelecypods, gastropods, scaphopods, and algae in the Queen. Kenji Konishi (oral communication, 1960), of the Geological Survey, identified the algae ?Gyymnocodium sp. and Mizzia sp. in thin sections of samples of the Queen from North McKittrick Canyon (stratigraphic sections 20 and 21, pl. 3).
Fossils are rare or absent in the Seven Rivers, Yates, and Tansill Formations near their transition into the evaporite facies, but they become increasingly abundant toward the Capitan Limestone. Even where relatively abundant, however, the fossils are dolomitized and commonly fragmental. None were collected during the present investigation. P. B. King (1948, p. 79-82) has presented a summary of the paleontology of the Carlsbad Limestone of former usage which was comprised of the same rocks.
Fusulinids of the genus Polydiexodina are abundant in the Seven Rivers, Yates, and Tansill Formations near the Capitan Limestone and locally form fusulinid coquinas. Other fusulinid genera are present but are rare. Other than fusulinids, pelecypods, gastropods, and scaphopods are the most abundant fossils found in the upper three formations of the Artesia Group. Brachiopods are present, but are much scarcer than in the Capitan Limestone or equivalent rocks of the Delaware basin. Sponges, cephalopods, and trilobites have been found also, but they are not abundant.
P. B. King (1948, p. 79) listed a dozen species of algae that had been identified from the carbonate facies of Seven Rivers, Yates and Tansill (Carlsbad Limestone of former usage). In addition to these, Kenji Konishi, of the Geological Survey (oral communication, 1960), found Permocalculus sp. in a thin section of a sample from the base of the Seven Rivers Formation in North McKittrick Canyon (stratigraphic section 21, pl. 3). Some workers (Ruedemann, 1929, p. 1079-1080; Johnson, 1942, p. 213; Newell and others, 1953, p. 120) believe that the pisolites of the carbonate facies of the Artesia Group may be of algal origin.
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