Coral
Lophophyllidium.
The early Permian seashore, where limy muds beyond the surf intermingled with red sandy muds swept from the north, vacillated somewhere north of Alamogordo with each sea-level change. Amid the breakers, and as submarine banks in the shallow waters, reefs grew—moundlike masses of shell debris and calcite mud trapped among frondlike calcareous algae. Near Tularosa, these algal “bioherms” are sixty feet high and extend within broad belts half a mile wide. In southeastern New Mexico, these buried “Abo” reefs have yielded much oil.
By the middle of Permian time, the southern Colorado mountains had been worn down to low hills that lay north of an extensive sea covering most of New Mexico. From Santa Fe south to White Sands and southeastward almost to Carlsbad, very shallow marine waters were alternately stifled by pale-red sandy muds or evaporated by the sun. The results were alternating beds of pale-red sandstone, gypsum, and silty dolomitic limestone, called the Yeso Formation. Locally, as near Carrizozo, thick deposits of rock salt also were precipitated, and the Yeso there is about 4000 feet thick. At this time, the Delaware basin of southeastern New Mexico saw the beginning of its most spectacular events, the building of the Capitan and Goat Seep reefs. This basin—a huge oval south of Carlsbad and east of Carlsbad Caverns—had been “deep” sea during most of Pennsylvanian time, but it was a more distinct geographic feature during the Permian. While the pale-red sands, gypsum, halite, and dolomitic limestones of the Yeso Formation were laid down to the north and northwest, the Delaware basin was rimmed by a low, broad bank of fossil-hash calcite sand, now called the Victorio Peak Limestone. In the basin, in deep stagnant waters, black sandy limestone and black shale of the Bone Spring Formation were deposited.
A sheet of white quartz sand filled the late Yeso seas; the resulting Glorieta Sandstone, about 200 feet thick, prominently caps Glorieta Mesa. Its cliffs are a familiar sight to travelers on the Santa Fe Railway at Glorieta Pass. The Coconino Sandstone in the Grand Canyon area of Arizona is the western part of the Glorieta. This “clean” sand—lacking intermixed mud—marks the continued lowering of the southern Colorado uplands. Broad seas then spread over all but northern New Mexico and a thick (600 to 1000 feet) persistent marine unit, the San Andres Limestone, was laid down. Much oil is produced in southeastern New Mexico from this dark-gray unit of limestones and dolomites. The rich agricultural region stretching from Roswell to Artesia depends on underground water gained from the San Andres Limestone, water that falls as rain and snow on the Sacramento Mountains, seeps underground into the cracks and caverns within the San Andres, and flows eastward downslope to the Pecos Valley.
The delicate balance between land and sea swung upward at the end of San Andres time as these late Permian seas retreated to southern New Mexico. The deep Delaware basin was the only persistent marine body of water. It was rimmed by magnificent towering barrier reefs, the Goat Seep and Capitan reefs that now are host to Carlsbad Caverns. These reefs were similar to the present-day Great Barrier Reef of Australia, except that the Capitan and Goat Seep reefs surrounded an inland sea whereas the Australian reef borders a continent. The Capitan reef is about 400 miles long, and other than oceanward channels cut through to the south, completely encircled the 10,000-square-mile Delaware basin. At its heyday, the Capitan reef was barely awash, and teeming with life, in contrast to the silent, stagnant deeps of the Delaware basin which were about 2000 feet below sea level only a few miles away from the barrier reef. On the steep slope into the basin, huge slump blocks of fossiliferous reef limestone slid, mingling with fossil-hash sand. These “flank” beds dip steeply from the massive reef core to interfinger with the black sandy limestones of the basin.
The Delaware basin was a marine feature throughout Late Paleozoic time; its northwestern border is now marked by the southeast-trending front of the Guadalupe Mountains southeast of Carlsbad; its north edge was east-northeast of Carlsbad, and it extended southward into West Texas.
Shallow “shelf” seas reached irregularly and intermittently northward and northwestward from the Capitan reef and mingled with low islands throughout all but southeastern New Mexico. Landward, away from the Delaware basin, the rocks change from massive, thick, light-gray limestones of the reefs into thin units of thin-bedded dolomite, then abruptly into alternating beds of gypsum and redbeds, the Artesia Group of rocks, and finally, marking the distant shorelines, into thin units of red mudstone and red sandstone, the Bernal Formation. Evaporation of sea water was excessive, and average temperatures high; the climate varied from semiarid in northwestern New Mexico to subtropical in the Delaware basin area—a contrast and a similarity to today’s climate.
Figure 9. Castile gypsum sample