Geological Survey Professional Paper 446 Geology of the Guadalupe Mountains, New Mexico

Very little is known about the Precambrian history of the Guadalupe Mountain region. Granitic and metamorphic rocks in the Precambrian in several deep wells suggest that the region was part of an ancient orogenic belt. By analogy with dated Precambrian rocks of similar lithology elsewhere in New Mexico and in western Texas (Jaffe and others, 1959) these rocks can probably be classified as less than one billion years old. There is no record of the latest Precambrian or most of Cambrian time in the area; however, the area was reduced to a nearly level plain on which Paleozoic rocks were later deposited.

During most of the Paleozoic Era, until near the end of the Mississippian Period, the present report area was part of a broad low-lying stable region that was intermittently covered by shallow seas. The marine invasions resulted in the deposition of about 2,500 feet of predominantly carbonate rock from the base of the Bliss Sandstone to the top of the Helms shale.

Early in Pennsylvanian time, after a half billion years of stability, submarine tectonism began in the report area. Intermittently throughout Pennsylvanian time the southwestern part of the area was elevated relative to the northeastern part along the northwestward trending Huapache thrust zone. The uplifted area is probably a southeastern branch or extension of the Pedernal uplift of central New Mexico (fig. 3). Within the report area, uplift was apparently greatest in the north. Most of the uplift probably took place beneath seas that had advanced over the area early in Pennsylvanian time and that had fluctuated in depth. Periodically, submarine or subaerial erosion took place on the higher areas, and reworked sediments were dumped in the lower areas adjacent to the fault zone. Concurrent with movement along the Huapache fault zone, local bulging of the sea bottom in the deeper part of the sea to the northeast produced variable thicknesses of Pennsylvanian sediments. Toward the close of Pennsylvanian time or very early in Permian time, tectonic activity virtually ceased, and mixed continental and marine sediments were deposited in the lower areas nearly obliterating the irregular sea-bottom topography caused by the tectonism. Either the area southwest of the Huapache thrust zone remained slightly higher than the area to the northeast, or there was minor renewed movement along the thrust zone early in Permian time, resulting in a somewhat greater accumulation of sediments of Wolfcamp and early Leonard age northeast of the old uplifted area than on the uplifted area.

Concurrent with beginning of Early Pennsylvanian tectonism, the Delaware basin may have begun to subside, but it was during Wolfcamp time that the basin first began to assume a definite shape. The northwest margin of the basin still was not sharply defined, however, and it is reflected today by the broad facies change from dolomite of the Hueco Limestone of the Northwest-shelf area to limestone and shale in the basin.

The Delaware basin subsided farther in Leonard time, and the northwest margin of the basin became more definite in form, possibly because of incipient movement early in the epoch along the line of the Bone Spring monocline. Along this hinge line, great submarine-bank deposits of the Victorio Peak Limestone were laid down. These deposits apparently formed a barrier to free circulation; black shale and fetid limestone of the Bone Spring Limestone were deposited in the basin simultaneously with deposition of the dolomite,⁴ siltstone, and evaporites of the Yeso Formation in the shelf area.

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⁴According to Adams and Rhodes (1960), these shelf dolomites of Permian age were originally deposited as calcium carbonate and then altered to dolomite by highly magnesian lagoonal waters refluxing to the basin.

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At about the end of Leonard time pronounced differential movement occurred along the basin margin, and the Bone Spring arch was elevated, forming a barrier, 15 to 20 miles wide, between the Delaware basin and the Northwest-shelf area. A marked change in sedimentation ensued. Black shale and limestone deposition in the basin was followed by deposition of sandstone and siltstone of the Brushy Canyon Formation which lapped onto the eroded edge of the Bone Spring monocline. Meanwhile, virtually clastic-free carbonate of the lower part of the San Andres Limestone was deposited in the shelf area northwest of the Bone Spring arch. By the end of Brushy Canyon time, relief on both sides of the Bone Spring arch was masked by on-lapping sediments. Sand and silt of the lower part of the Cherry Canyon Formation were then deposited in the basin and over the southeastern part of the arch, and these sediments merged northwestward with the simultaneously deposited carbonates in the upper part of the San Andres Limestone. The source of the sand and silt of the Brushy Canyon Formation and lower part of the Cherry Canyon Formation is unknown. Contemporaneous deposition of carbonate rock to the northwest seems to preclude the possibility of a source in that direction as suggested by King (1942, p. 31). Newell and others (1953, p. 94) and Hull (1957, p. 297) have presented evidence that turbidity currents played a role in the deposition of sediments of the Delaware Mountain Group. Perhaps sediments of the Brushy Canyon and the lower part of the Cherry Canyon were carried into the basin by turbidity currents from an unknown source to the south.

Near the end of San Andres time or early in Cherry Canyon time, local uplift along the northwest edge of the Bone Spring arch resulted in the erosion of the upper part of the San Andres and Cherry Canyon transition zone before Grayburg deposition. At the same time the Bone Spring monocline may have been slightly rejuvenated, thus emphasizing the hinge line of the basin margin. Conditions were established that led to the accumulation of the lime-bank deposits of the lower part of the Goat Seep Dolomite directly on the Bone Spring monocline. In turn, these deposits formed a foundation for the growth of a barrier reef, represented by the upper part of the Goat Seep Dolomite. Near the beginning of Goat Seep deposition, quartzose clastic sediments began to be carried into the area from the northwest for the first time since deposition of the Yeso Formation, and they are preserved as sandstone and siltstone beds in the Grayburg and Queen Formations. The source of these clastics may have been the distant Uncompahgre highland (fig. 3). Highlands nearer to the report area, such as the Pedernal uplift, apparently had been buried by earlier Permian sediments. Some of the clastics apparently washed over and through gaps in the barrier reef at the basin margin, but, in general, the bank and reef of Goat Seep age probably formed a fairly effective barrier to passage of clastics into the basin. The silt and sand of the upper part of the Cherry Canyon Formation that were deposited at the same time in the basin were probably still being derived, in large part, from source areas to the south. The great lime bank and reef barrier at the basin margin also restricted the flow of water from the basin to the shelf. This restriction of circulation, coupled with evaporation, led to the precipitation of calcium sulfate on the shallow lagoon floor about 15 to 25 miles shelfward; at the same time limy mud and sand were deposited closer to the reef zone. Just before the end of Cherry Canyon time, a slight lowering of sea level or a slight raising of the basin margin apparently caused a brief cessation of reef growth, and the highest beds of the Cherry Canyon and Queen Formations lapped onto both sides of the dead reef.

Shortly thereafter, at the beginning of Bell Canyon time, conditions again favored reef growth, and the reef limestone that makes up the massive member of the Capitan Limestone began to grow upward and basinward from the top of the Goat Seep Dolomite. Details of the formation of the Capitan Limestone and its shelf and basin equivalents have been described by many workers (Lloyd, 1929; Adams and Frenzel, 1950; Newell and others, 1953),⁵ and are summarized here with a few additional ideas.

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⁵Other origins for the Capitan Limestone have been postulated by Cave (1954) and Moore (1959).

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During part of Seven Rivers time and during Tansill time, the reef grew upward more than basinward, but in most of Seven Rivers time and in Yates time, it grew basinward at a much faster rate than upward. This obliquely upward growth of the reef indicated to Newell and others (1953, p. 106-107) that subsidence of the basin margin was slow relative to the rate of reef growth resulting in the reef (massive member) growing out over its own talus (breccia member). The relatively rapid outward growth, which would tend to leave the most seaward part of the reef unsupported, may also explain the greater abundance of reef talus than of reef rock. It is also possible that the frame-building algae, sponges, and bryozoans of the Capitan did not form as rigid a framework as is found in many modern reefs; this comparative lack of rigidity might cause the reef to break up into talus more readily.

The probable northwestern source area of quartzose clastic sediments diminished greatly in importance at the end of Queen time, and during Seven Rivers time contributed very little sediment to the shelf area. At the same time, the probable southern source of basin sediments may have decreased its output as reflected by a relatively small amount of clastic rock between the base of the Bell Canyon Formation and the Rader Limestone Member. Carbonate deposition, however, continued in the shelf area near the reef zone and almost kept pace with reef growth. In the shallow lagoonal waters adjacent to the reef, bioclastic carbonate debris, pisolites, and oolites accumulated. Farther from the reef, carbonate mud was the chief sediment. Several miles back, evaporation exceeded replenishment of water from the basin, and the evaporite deposits of the Artesia Group were deposited by precipitation.

An influx of quartzose sediment from the northwest occurred in Yates time. Much of this sediment was trapped behind the reef and remains as the sandstone and siltstone beds of the Yates Formation, but much also apparently washed over and through gaps in the reef. In the process of washing over the reef, natural cavities in the reef rock were filled by clastic sediments, and much of the sediment also apparently got through the reef to the basin to mix with clastic sediments possibly still being contributed from the south. This is suggested by the large proportion of clastic rock in the part of the Bell Canyon Formation equivalent to the Yates between the Rader and Lamar Limestone Members. In addition to pockets and stringers of sandstone in the reef, evidence that much of this quartzose sediment washed over and past the reef is indicated by the close similarity of sandstone of the Yates and Bell Canyon Formations, and by the pinchout of sandstone beds of the Bell Canyon between foreset beds of limestone in the breccia member of the Capitan Limestone. During intervals of Yates time when quartz sand and silt were not being brought into the lagoon in volume, limestone and evaporite deposition took place much as it had during Seven Rivers time. Conditions during Tansill time repeated those of Seven Rivers time, and very little quartzose sediment was deposited.

As the reef of Capitan age grew, deposition in the basin proceeded at a slower rate than on the shelf and did not keep up with sinking of the basin. Consequently, the sea became progressively deeper in the basin throughout most of Bell Canyon time. Newell and others (1953, p. 69-77) have demonstrated that large submarine slides occurred in partially consolidated Bell Canyon sediments on the basinward slope away from the reef. By the end of Capitan time the sea bottom in the Delaware basin is estimated to have been about 1,500 feet lower than the lagoon floor adjacent to the reef on the northwest.

Near the close of Capitan time, access of water to and from the open ocean became restricted, the seas of the shelf dried up, and the water of the Delaware basin became more saline, causing the end of reef growth. The few feet of nonfossiliferous limestone at the base of the Castile Formation probably resulted from the initial evaporation of the restricted water. Udden (1924) interpreted each pair of anhydrite and limestone laminae in the lower part of the Castile as annual layers resulting from seasonal variations in salinity. The warming of surface water in summer would result in the loss of carbon dioxide and the consequent decrease in solubility of calcium carbonate. Thus, the limestone laminae, which are high in organic content, are thought to represent warm-season deposition; whereas the intervening calcium sulfate laminae were deposited in the colder seasons. R. H. King (1947, p. 470) suggested that "the water within the basin consisted of a body of brine lying below average wave base and a less dense surface layer lying above average wave base" and that the barrier which closed off free circulation between the Delaware basin and the open sea to the south either had a top which "lay partly below wave base or the barrier was permeable." The relatively fresh surface waters of the basin were continually replenished from the open sea while the denser brines below drained out to sea over or through the barrier. Scruton (1953, p. 2502, 2510) accepted R. H. King's mechanism in principle, but suggested that the barrier to brine escape may have been in part dynamic; that is, outward flow of heavy brines may have been retarded by "pressures due to hydrostatic head and density distribution, friction between currents flowing in opposite directions, and friction between the deep current and the channel bottom." R. H. King (1947) believed that the few beds of halite in the Castile were deposited at times when the outflow of heavy brines was retarded or stopped. Scruton (1953) thought that variations in precipitation, temperature, sea level, and wind stress could also have contributed to vertical changes in sequence of evaporite beds.

By the close of Castile time, the Delaware basin was nearly filled with evaporite sediments, saline waters spread over the shelf areas for a unknown distance, and extensive salt deposition began resulting in the predominantly halite Salado Formation. That the replenishing waters of the open sea still apparently came from the south is suggested by greater amounts of the least soluble salts, such a calcium carbonate and calcium sulfate, far to the south in Texas; whereas the extremely soluble salts, such as sylvite and carnallite, are much more abundant in then northern part of the Salado Formation in New Mexico. Periodically during Salado time, clastic material swept far into the saline sea from the north and northeast leaving widespread but very thin beds of clay, silt, and sand. Toward the close of Salado time the influx of clastic material increased. Rustler time is marked by a great increase in clastic deposition and a concurrent freshening of the waters as reflected in a marked decrease in the relative abundance of halite and an increase in the proportion of carbonate rock. Broad epeirogenic uplift at the end of Permian time caused the seas to retreat, leaving the entire region above sea level.

Triassic or Jurassic rocks are not present in the report area, but the distribution of these and younger rocks elsewhere in New Mexico, Texas, and Mexico indicates that the area was above sea level throughout the Triassic and Jurassic Periods and into the Cretaceous Period. The area may have received flood-plain deposits in Late Triassic time (McKee and others, 1959, pl. 9), but, if so, they were stripped off and shed northward or southward during the Jurassic.

Late in Early Cretaceous time, shallow seas once again advanced over the area from the south but early in Late Cretaceous time probably retreated for the last time. Fossiliferous limestone and coarse sandstone and conglomerate were left behind to record this incursion of the sea. There is no record of most of Late Cretaceous time in the area. Probably the area was slightly above sea level.

Probably late in the Cretaceous Period or very early in the Tertiary Period the entire region was elevated by broad epeirogenic uplift and was tilted slightly to the northeast, and the report area apparently was subjected to mild tectonism. The three small igneous dikes in the area may have been intruded during or following these events. The tectonism produced the Walnut Canyon syncline, Guadalupe Ridge anticline, and related features. The stage was set for the establishment of the ancestral northeast-flowing drainage system. Black River, Walnut Creek (p. 47), Dark and Last Chance Canyons, and Rocky Arroyo probably originated at this time, and the caves in the limestones of Permian age began to form from phreatic solution.

During the Pliocene Epoch, the continental Ogallala Formation was deposited east of the present Pecos River, but it is not known whether or not any part of the present report area was once overlain by sedimentary rocks of the Ogallala. Thin remnants of siliceous conglomerate on top of the Guadalupe Mountains are interpreted in this report to be of Cretaceous age, and if the Ogallala was ever present, it has been removed by erosion.

Most of the faulting and main uplift of the Guadalupe Mountains probably occurred late in the Pliocene and early in the Pleistocene. The present drainage system and landforms, the Quaternary piedmont and alluvial deposits, the calcareous tufa accumulations, and most of the cave decorations have formed since the mountain uplift and are still being modified. Rates of erosion, deposition, and carbonate precipitation, both on the surface and in the caves, have fluctuated considerably with the climatic cycles, which, in turn, probably were controlled by the advances and retreats of continental glaciation to the north.