What did West Texas and New Mexico look like during the Permian, 260 million years ago? That’s the question six Tennessee Tech earth science students attempted to answer on a nine-day field trip, May 23-June 1, 2013. Over the course of the spring semester, GEOL 4810 students Kolbe Andrzejewski, John Baird, Geoff Gadd, Joe Kalbarczyk, Jordan Sachs, and Paul Woods became experts on Permian depositional environments. Then, they headed west to find out what’s in them there western hills?
After two days of crossing the U.S., the group arrived at the Carlsbad KOA in New Mexico just in time for a desert thunderstorm with hail and high winds. It turned out to be the only precipitation students saw until the drive back east. Temperatures in the desert hovered in the 90s during the days and cooled off into the 60s at night.
As the trip progressed, the group explored a series of depositional environments from the Permian, including: (1) carbonate back-reef, reef, and fore-reef deposits; (2) carbonate and clastic slope rocks; (3) clastic deepwater formations; and (4) evaporite deposits. The group also made stops at Carlsbad Caverns to view karst features and the Permian Basin Petroleum Museum to learn about oil/gas exploration in the prolific reservoir system.
To view the complete route map with geologic stops in Google Maps, click here.
DAY 1: Back-reef deposits
Led by Kolbe Andrzejewski, the first day of field work focused on facies and deposits of a back-reef environment. Stops 1 and 2 were located approximately 12 miles landward (northwestward) of the Guadalupean fault scarp, the modern-day expression of the ancient reef front. The group began by describing dolomite wackestones exposed in a dry desert riverbed known as Rocky Arroyo. At a second stop closer to the shelf edge, prominent dolomite outcrops contained abundant algal stromatolites but few other fossils.
After lunching in the shade of the van, the group drove south of Carlsbad to Dark Canyon, where the carbonate facies were strikingly different. Located approximately 1 mile from the reef front, the rocks of Stops 3 and 4 were well-bedded pisolitic dolomite grainstones.
DAY 2: The Reef – Guadalupe Peak Trail
The group got an early start on June 27th, and Day 2 was spent hiking Guadalupe Peak Trail in Guadalupe Mountains National Park. Although collecting rocks in the park was prohibited, folks had an opportunity to see spectacular rhombohedral calcite crystals along the hike. At the summit and on the descent, Geoff Gadd led discussions about reef and slope facies of the Guadalupe trail and ancient carbonate system.
After a full day of hiking and investigating carbonate rocks, everyone was pretty hungry and ready to sample the local cuisine. Although skeptical at first, it was determined that the restaurant below did, indeed, have “The Best Mexican Food in Town”.
DAY 3: Walnut Canyon and Carlsbad Caverns
On Day 3, students enjoyed a brief respite from the desert sun. The first stop of the day was located at the mouth of Walnut Canyon, on the road leading to Carlsbad Caverns. Here, poorly bedded lime grainstones cropped out, complete with calcite-filled veins and joint sets.
Also along the entrance highway, the group stopped for a glimpse of teepee structures in the carbonate beds and to admire abundant pisolite grainstones.
Folks enjoyed a quick lunch at Carlsbad Caverns prior to spending the afternoon underground. Jordan Sachs, an avid caver and TTU student, gave a thorough introduction on the local karst system and led group discussions, pointing out cave formations and features in the subsurface. A general consensus was reached that geologists love food, hence textural names for precipitating minerals like cave bacon and popcorn.
DAY 4: McKittrick Canyon and the Permian Reef Geology Trail
Over the course of the first three days, students had worked their way from the back-reef to the carbonate reef environments of the Permian. On Day 4, Joe Kalbarczyk led the group up the Permian Reef Geology Trail, located in Guadalupe Mountains National Park. One of the most spectacular geo-trails in the world (how often can you actually hike up an ancient clinoform?!), brochures and a full guidebook are available on the geology of this route.
At the top of the trail, students ate lunch on the nose of the ancient reef, looking southward into the basin.
DAY 5: Evaporites, deepwater deposits and salt flats
The last field day was spent on the south side of the Guadalupe Fault scarp, exploring different types of basin fill that accumulated in the Permian. Led by Paul Woods, the first stop of the day was in the Castile Formation, which is characterized by couplets of gypsum and organic-rich micritic mud. These evaporites mark the transition from the Middle (Guadalupean) to Late (Ochoan) Permian; they are interpreted to record increasing salinity in the basin as it filled and became more and more dessicated. To the east, the Castile serves as an effective seal rock in the Permian petroleum system.
At a second stop along Highway 180, boulder conglomerates outcropped approximately 7 miles from the ancient reef front. The giant clasts (some as large as a car!) contain carbonate lithofacies, which suggest they originated higher on the slope. Thus, they are interpreted to record mass transport processes, i.e. debris flows, that flowed into the basin.
The afternoon stops were spent south of the Guadalupe Fault scarp and looking back towards El Capitan and Guadalupe Peak. Deepwater clastic deposits of the Bell Canyon, Cherry Canyon and Brushy Canyon units were discussed and described by John Baird. The group identified incomplete Bouma sequences containing structureless sandstone, ripples and planar laminations.
Salt Flat, an area along Highway 180, served as the final field stop of the trip. Here, the group had time to observe modern evaporites, take in the West Texas vista, and contemplate the ancient Permian Basin System.
After five days investigating sedimentary rocks – clastics, carbonates, and evaporites – Tennessee Tech students and Dr. Wolak headed home to Cookeville. In Midland, TX, the Permian Basin Petroleum Museum offered an opportunity to review the geology through the lens of oil and gas exploration.
In addition to the spectacular geology and modern depositional environments, Tennessee Tech earth science students enjoyed a few other treats, including:
1.) Graffiti at Road Side BBQ in Memphis, TN
2.) Tarantula-viewing at the Carlsbad KOA entrance
3.) High Desert Fashion, the Tennessee Way
4.) Jumping for joy after a week in the field doing geology. Go Golden Eagles!