GEOLOGY OF THE GUADALUPE MOUNTAINS, NEW MEXICO
By PHILIP T. HAYES
The area described, nearly 1,000 square miles, lies in Eddy and Otero Counties along the south boundary of New Mexico and includes most of the northern part of the Guadalupe Mountains and a considerable area of plains.
Beneath the mapped area, but not exposed on the surface, are rocks ranging in age from Precambrian to Early Permian. Overlying the Precambrian rocks is the Bliss Sandstone of Ordovician age. The Bliss is overlain by the Lower Ordovician El Paso Formation. The El Paso, in turn, is overlain, in the eastern part of the area, by a unit which is tentatively correlated with the Middle Ordovician Simpson Group of Oklahoma. Under much of the report area, however, the El Paso is overlain by the Montoya Dolomite of Late Ordovician age. Above the Montoya is the Fusselman Dolomite of Silurian age, which is overlain by a unit that is tentatively correlated with the Percha Shale of Late Devonian age. Above the Percha (?) is cherty limestone of Mississippian age, which is overlain by a unit correlated with the Upper Mississippian Helms Formation. Pennsylvanian rocks in the report area range in thickness from 0 to more than 4,000 feet. Both the lithology and thickness of the Pennsylvanian rocks were influenced by Pennsylvanian tectonic movements within the area and are highly variable.
Permian rocks of the area are divided from southeast to northwest into three facies: Delaware basin, basin margin, and Northwest shelf. The basin rocks are mainly confined to the subsurface, whereas the basin-margin and shelf rocks are widely exposed. In the basin, the lowest Permian rocks are referred to the Wolfcamp Series. Next above is the Bone Spring Limestone assigned to the Leonard Series. The Bone Spring is overlain by the Brushy Canyon, Cherry Canyon, and Bell Canyon Formations of the Delaware Mountain Group which is assigned to the Guadalupe Series. Overlying the Delaware Mountain Group is the Castile Formation of the Ochoa Series. A solution breccia which was mapped with the upper part of the Castile Formation probably represents the Salado Formation. This breccia is overlain by the basal part of the Rustler Formation of the Ochoa Series, the youngest Permian formation in the area.
In the basin-margin area, the Wolfcamp Series is represented by a broad transition zone in which rocks of the basin facies grade into all but the uppermost part of the Hueco Limestone of the Northwest-shelf area. The Leonard Series in the basin-margin area is represented by the Victorio Peak Limestone and Cutoff Shale. An unconformity representing Brushy Canyon time separates the Cutoff from the overlying shelfward-projecting sandstone tongue of the Cherry Canyon Formation. This tongue is overlain by the Goat Seep Dolomite which grades basinward into the Cherry Canyon Formation. The Goat Seep is overlain by the Capitan Limestone. The Capitan is subdivided into a massive member and a breccia member which are transitional into one another both laterally and vertically. The breccia member grades southeastward into the Bell Canyon Formation of the Delaware basin.
In the Northwest-shelf area the lowest Permian formation is the Hueco Limestone. Most of the Hueco is equivalent to basin rocks of the Wolfcamp Series, but the uppermost part may be of early Bone Spring age. Overlying the Hueco is the Yeso Formation which is laterally equivalent to most of the Victorio Peak Limestone. Above the Yeso is the San Andres Limestone. The basal part of the San Andres may grade into the uppermost part of the Victorio Peak; part of it grades into the Cutoff Shale. The medial part of the San Andres apparently has no equivalent in the basin-margin area and seems to be equivalent to the Brushy Canyon Formation of the Delaware basin. The uppermost part of the San Andres grades laterally into the sandstone tongue of the Cherry Canyon Formation. Shelf rocks equivalent to the Goat Seep Dolomite are the Grayburg and Queen Formations which are the lower two formations of the Artesia Group. The Queen is overlain by the Seven Rivers, Yates, and Tansill Formations, which are the upper three formations of the Artesia Group and are laterally equivalent to the Capitan Limestone. The carbonate facies of the Artesia Group, near the basin margin, grades laterally northwestward into an evaporite facies within which the five formations are also distinguished.
Fragments of rock remaining from an ancient sinkhole fill in the Castile Formation contain Cretaceous fossils. Conglomeratic sandstone found in the Guadalupe Mountains in sandstone dikes and shallow sink fills also may be of Cretaceous age. Three small igneous dikes constitute the only Tertiary rock exposed in the area. Quaternary deposits include gravel of Pleistocene age, and alluvium and calcareous tufa deposits of Recent age.
The oldest known structural feature in the report area is the buried northwestward-trending Huapache thrust-fault zone of Pennsylvanian age. The southwest side of the zone was uplifted relative to the northeast side intermittently throughout Pennsylvanian time. The resultant relief had a profound effect on Pennsylvanian sedimentation and also seems to have affected Lower Permian sedimentation. During the Permian the Bone Spring arch formed in the shelf area along the margin of the Delaware basin. This arch strongly influenced Permian deposition. Cenozoic structural features include folds, faults, joints, and unusual linear features in the Castile Formation. Early Cenozoic folding resulted in anticlines and synclines approximately parallel to the trend of the Capitan Limestone. Probably late in the Cenozoic, concurrent with the main uplift of the Guadalupe Mountains, a monocline and closely associated dome were formed over the old Huapache thrust zone. Most of the faulting in the area also occurred during the uplift of the mountains. The faults, all of which are in the western part of the area, are nearly all normal and trend north to northwest. The largest faults have stratigraphic displacements of about 800 feet.
The youthful to mature landforms and the drainage of the area are directly related to the structure and character of the underlying rocks, but they may be partly controlled by an old superimposed drainage system. An extensive limestone cave system, which includes Carlsbad Cavern, was developed principally during an earlier erosion cycle and has been partly exhumed by the modern drainage system.
The earliest geologic event indicated in the area is a probable orogeny that occurred relatively late in the Precambrian. During latest Precambrian and earliest Cambrian time, the area was reduced to a peneplane. From very late in the Cambrian Period or very early in the Ordovician until the end of the Mississippian, the area was inundated by several incursions of shallow seas. Faulting and, possibly, folding occurred during the Pennsylvanian Period and affected Pennsylvanian and Early Permian sedimentation. Sinking of the Delaware basin may have begun in the Pennsylvanian Period or somewhat earlier, but its effects on sedimentation within the report area were most pronounced in the Permian. Differences in depositional environments between the Northwest-shelf area and the basin are reflected by facies changes in Permian rocks. While dominantly clastic sediments were being deposited in the basin, dolomite, limestone, siltstone, and evaporites were deposited on the shelf to the northwest. The intervening basin-margin area was at various times the site of lime-bank deposition and barrier-reef growth. Deposition in the basin-margin area was affected by intermittent mild folding. Toward the end of Permian time the waters of the Delaware basin became more saline, thus causing the end of barrier-reef growth at the basin margin. Evaporite deposits filled the Delaware basin, after which evaporites, dolomite, and clastics were deposited over the basin and the adjacent shelf. The area probably remained above sea level from latest Permian time until late in Early Cretaceous time when a shallow sea apparently advanced over the area once again. This sea retreated early in Late Cretaceous time. Late in the Cretaceous Period or very early in the Tertiary Period, the area was affected by broad epeirogenic uplift. Following this uplift, the ancestral drainage of the area was established and cave solution began. The main uplift of the Guadalupe Mountains probably took place late the Pliocene or early in the Pleistocene, and the present geomorphic features have evolved since that time.
Small amounts of oil are produced from the Bell Canyon Formation in the Black River field. Elsewhere, commercial quantities of gas have been discovered in Pennsylvanian rocks in several wells. About 70 unsuccessful exploratory holes have been drilled in the report area. Most of these are shallow holes drilled in the Delaware basin. Important reserves of oil may be present in the Delaware basin and in the shelf area. Mineral deposits of potential value include gypsum and sodium sulfate. Ground-water availability in the area is variable, depending on local geologic conditions. In some areas, ground water is virtually nonexistent, whereas, in others, considerable quantities of water of fair quality are available at shallow depths.
Last Updated: 13-Feb-2008