Our first day of this journey was primarily a day of travel and coordination. I, along with my sedimentary petrology classmates and Dr. Bogdan Onac of University of South Florida, departed Tampa International Airport by our airlines of choosing to rendezvous in El Paso, Tx. The purpose of this field trip was to explore and investigate the geology of remanants of the ancient Permian Sea in Texas and New Mexico. However, we also explored other adjacent geologically important rift zones and salt basins. Since the majority of the day was our travel to Washington Ranch where we would be camped for the duration of the trip, I would like to take this opportunity to give you a brief overview of the geologic history and composition of the areas we traveled to. Coming from the relatively flat landscape of Florida, we were immediately placed in a much more tectonically affected area once arriving in El Paso.
After we made our way past the El Paso city limits we began heading toward the southern end of the Hueco Mountains and along the Hueco Bolson to the Diablo Platform (graben). At the base of the Hueco Mountains we made our first stop of the trip to investigate the bedding layers visible in the mountains around us (mile 24.9). These formations were composed of primarily Magdalena Formation (Carboniferous limestone/dolomite) at the base with a small cap of Permian Formation. The bedding layers had a tilt to them which helped indicate the presence of tectonic activity. This area is a part of the Basin and Range Province (a large series of horst and grabens) which I will talk about repeatedly across the duration of our field trip. The basin and range system consists of highly active tectonics that are largely accounted for by (1) the large rift zone of the Rio Grande Rift (expansion and faulting), (2) the Pedernal Uplift (anticline fold axis) which caused the increased uplift of the Diablo platform, (3) and the normal faulting occurring at the Salt Basin/Guadalupe Mountains fault zone. On our route to Camp Washington we traveled through all of these different geomorphologies. We traversed across the Diablo Platform, passed through the Salt Basin (graben), and then began our ascent of the Guadalupe Mountains (horst). Here are a few images that help to visualize this activity.
Example of the tectonics involved at the basin and range system provided by Dr. Onac.
Cross-section of the route traveled from El Paso to the Guadalupe Mountains provided Dr. Onac helps to visualize the tectonics and geology occurring along the route.
While finally approaching the Guadalupe mountains the change in geologic landscape was quite noticeable as we left the Diablo Platform and entered the Salt Basin. The Salt Basin would be our first, but not last, introduction to the Delaware Basin along our trip. And so, we made our second stop to get out and inspect what we were seeing in the sediments and topography/geology of the land surface in the area. The white color sediments and rocks (evaporites) and secondary mud crack formations were a clear indicator that we entered our first location that showed evaporite processes.
The Salt Basin Graben with the Guadalupe Mountains (horst) in the background.
Classmate examining the evaporite sediments.
Mud cracks found at the surface is a secondary formation caused by the wetting and drying of the sediments. These features are a good indicator of which way is up on of bedded areas that may have been tectonically altered.
After our stop at the Salt Basin, we made our final stop of the day before reaching camp at the El Capitan overlook. This was our first introduction into the Guadalupe Mountains and would provide our first view of the upper Permian Shelf and Basin (from a distance). Here are a few images to clarify.
El Capitan from the overlook. It was a little overcast that day. This is part of the Capitan Reef Formation which will be discussed in detail.
Since it was overcast, and raining sporadically, we decided to go ahead and travel the rest of the way through the Guadalupe Mountains to Camp Washington near Carlsbad. After a long day of travel, I was excited to get out and situated in preparation for our explorations that laid ahead.
Dr. Onac and my classmates at dinner once arriving to the ranch.
Our second day brought us to Guadalupe National Park to hike (my favorite hobby) the Permian Trail. This hike begins at McKkitrick Canyon and ascends up the Guadalupe Mountains towards Capitan Reef. The trail has a series of marked points along your way which allow you to see many of the major geologic features viewable in the canyon. Since I am going to give you a brief description of each stop along the way, I would like to first give you a general overview of the area before talking about our ascent up the trail.
McKkitrick Canyon viewed from the Permian Trail.
The trail journeys through multiple carbonate environments and formations as we make our ascent up. From the base of the trailhead you can observe 4 distinct formations. Each formation represents a different carbonate environment. The Tensill and Yates formations represent the backreef and forereef environment. These two formations are located at the highest elevations(backreef), behind the Capitan Reef, as well as just below the reef at lower elevations along the shelf slope(forereef). The Captain Reef is the main upper unit. The lowest of the unit of the shelf is the 7 Rivers Formation. When you are siting at the trailhead you are standing on what is the Cherry, Brushy, and Bell Canyon formations we observe on the following days’ travels to the roadcuts and outcrops. The Permian Geology Trail allows you to traverse up the Permian Shelf from the Delaware Basin to the Capitan Reef enabling you to see the different compositional strata layers and also to observe the difference in deep time environmental evidence as well. The shelf itself was formed around the same time as the overlying reef (Gaudalupian), however, the shelf contains many siliciclastic differences that the overlying reef doesn’t contain. These are due to the differences in depositional environments. Here are a few images to clarify the area.
Stop1: The first stop on the trail exhibited oligomictic conglomerates that were intraformational and had calcareous cement. They were Quaternary in age and formed by the percolation of water from the McKkitrick Canyon waterflow.
Stop 2: There was a compostional change at this location. These formations were darker colored wackestones. Some areas had chert inclusion. You were able to observe fossils with silica replacement in many rocks. Bedding was well uniformed. This wackestone is part of the Bell Canyon Formation. Other structures visible in some of the bedding layers were stillolites and organism boreholes (bioturbation).
Stop 3: Bedding layers and rocks showed higher skeletal and non-skeltal grain clast composition. Looked to be a packestone that most likely formed because of turbidity currents. Based this origin on the differing compostion of some clasts visible.
Stillolites (pressure deformation) in the Bell Canyon wackestone.
Intraclastic limestone formed by the introduction of clasts of different limestone compositions. Result of turbidity currents. The darker colored clasts differ in composition from the surrounding clast.
Silicified crinoids were more resistant to weathering than the surrounding carbonate rock.
Stop 4: At the fourth stop we started to observe a variety of different compositional layers. Mudstones, wackestones, and packstones were all present. Different rocks present due to turbidity currents. Lots of bioturbation present. Some areas of wackestones and packstones were so highly bioturbated that you couldn’t observe layering or foliation.
Cross-cut containing mudstone, packstone, and wackestone layers.
Bioturbation has caused the bedding layers to be indistinguishable.
Stop 5: This stop exhibited a large eroded and weathered column of wackestone with two distinct layers. The top layer was highly weathered an bioturbated whereas the bottom section was less weathered and bioturbated. In addition, there was evidence of dissolution in the rocks and re-precipitation of the calcite after the weathering had occurred. In the distance, across the canyon, we were better able to observe the large bedding formations.
Karrens visible in this feature. The upper segment of this pinnacle was a highly weathered and bioturbated wackestone where the bedding layers were hard to discern. The lower section was a far less weathered and less bioturbated wackestone with noticeable thin bedding layers. The structure showed signs of dissolution and weathering where calcite had re-precipitated as a result.
Stop 6: Exhibited a high concentration of skeletal grains in between some bedding layers. The differing composition was again a result of higher flow turbidity currents.
Example of how the skeletal composition of the bed layering was in the rock.
Stop 7: At this stop we were able to observe a compositional transition as we were leaving the slope towards the forereef. There was an observable difference between the lower and higher bedding profiles. The lower profile contained thin bedding planes with less skeletal grains whereas the upper profile didn’t exhibit any layering. In additionn the upper layer had larger clasts (intraclast packstone).
Stop 8: I examined two different rocks. The first rock examined was a skeletal packstone containing bivalves and other skeletal grains. It also contained a higher percent of skeletal grains than the second rock examined. The second rock was an intraclast packstone composed primarily of intraclasts.
Stop 9: Began to see gravity flow mud deposits.
Stop 10: Lunch break
Our beautiful view at lunch.
Stop11: There was a non-uniform mixture of clasts as the slope due to turbidity currents. Some secondary calcite precipitation visible. Most rocks were packstones with both skeletal grains and intraclasts. Grains were well rounded (grapestones). Fossils present were algae, sponges, and corals.
Well preserved coral fossils observed.
Secondary calcite formation precipitated into fractures.
Mixture of sponges, algae and some corals.
Stop 12: There was no bedding visible. Observed a large bioconstruction boulder that was held together by sponges, algae and other fossils. The boulder had fallen from the reef down into the forereef and slope area.
Biocunstruction boulder that had transported down from the reef.
Stop 13: Highly fossiliferous muddy wackestones
Fossiliferous wackestone with fusilinids.
Stop 14: Exhibited horizontally cut fusilinids. This limestone formation had formed along the slope.
Point 15: This was the final point that we made it to and it marked the beginning of the reef formation. Many fossil varieties were present. Algea, sponges, brachiopods, and ammonites all were observed. This is where the Yates formation was about to begin. Unfortunately, time constraints meant that we had to end our hike here to start our descent back to the trailhead ensuring we would reach the camp in time for dinner.
We quickly made our descent and returned to the ranch area. However, first we stopped by the neighboring spring by that ranch which supplied water to much of the area. After we visited the spring we inspected rock formations that were directly behind our bunkhouses at the camp. They lied within a drainage channel that was connected to the springs drainage basin. After inspection we determined these rock structures to be tuffas. Tuffas as we know form around the mouths of spring areas.
Tuffa we observed located behind our bunkhouses at Camp Washington Ranch.
This was the completion of our second day. After nice hike and day spent in the sun, I was looking forward to the dinner and showers that awaited us.
The third day of our trip was spent visiting a variety of different formations that we were able to observe via roadcut outcrops. These roadcuts enabled us to be able to see a more detailed look at some of the formations we haven’t been able to view because they were always below the surface. Throughout the day we noticed that there was a high fluctuation in the compositions and variety of rock types from one roadcut to another. This was because these formations that occurred near the basin/slope interface or within the slope itself. This suggested that weren’t only carbonate formations, but also siliciclastic sandstone and shale formations. This was due to having undergone several (7 major) sea level fluctuations which allowed for the introduction and transportation of siliciclastic sediments to be deposited into the formation through large turbidity currents and underwater landslides. The majority of these road cuts were a part of the Delaware Mountain Group and are Guadalupian in age. We unfortunately weren’t able to arrange the stops in any progressive order to represent a natural progression through the vertical extent of a cross section of the Permian Basin area. So, I will post the stratigraphy of the basin area that I have already posted in a previous post for you to be able to reference as we move from roadcut to roadcut. I will do my best to be as clear as possible when discussing these but the order in which we observed them was very mixed so hopefully you can follow along.
Stop 1: Junction TX 54
This was not actually a roadcut stop but was a return to viewpoint of the south tip of the Guadalupe Mountains. This was the best location to be able to view the reef, forereef, and basin all in one sight.
The upper Capitan Formation (reef, forereef, and slope) is a limestone formation which overlies two lower distinguishable strata layers. Lower strata are the Cherry Canyon Formation sandstone and Brushy Canyon sandstone.
Rough sketch of the geology from the viewpoint.
The most important thing to note from what we viewed was the fact that the overlying formations viewed were the limestone formation of the reef and forereef and the lower formations were siliciclastic. The origin of the siliciclastic sediments in the basin formations we saw all came from erosional transportation from the North, Northwest, and Northeast during the major sea level change events.
Stop 2: Bone Spring Carbonates
Our first roadcut brought us to these thin bedded basin limestones. The bedding layers were fine grained micritic deposits lacking skeletal grains and had primarily a mud composition. They were dark in color which denoted a high organic content and were derived from gravitational suspension. There was evidence of some undulated beds (small folds) in which allowed for secondary calcite veins to form in the fracture voids. At 35 Ma years this formation is older than the reef. We weren’t able to find any, but it is possible to find Pyrite due to the high Fe content of the sediments.
Rough sketch of Bone Spring roadcut.
Stop 3: Brushy Canyon Formation
The Brushy Canyon outcrop had two different distinct strata. The upper unit was thick bedded brown sandstone layers which overlaid thin bedded shale and sandstone layers that were darker in color due to their higher organic content. There was some noticeable post-depositional undulations in the lower bedding units that suggest post depositional tectonic activity. On the right side of the outcrop the lower bedding abruptly ends due to channel filling resulting from erosional processes and channel filling. These strata represent the Lower Guadalupian Formation and formed at the same time the Capitan Reef was flourishing.
Right side of the Brushy Canyon outcrop where you can see the result of channel filling.
Rough sketch of Brushy Canyon outcrop.
Note the thin dark shale layers that alternate with the sandstone layers in the bottom unit. These indicate a short high organic event followed by a change in climate to allow for the shale to form. The shale forms from an environment that promotes anoxic conditions.
Stop 4: Upper Sequence of Brushy Canyon Sandstone
This sequence was a representative of channel and basin deposits. The alternating layers we observed were much thicker than the previous section of Brushy Canyon. This meant the environment was more stable for a longer period of time during their deposition. However, they still followed a repeated and alternating pattern representing major climate change events.
The tilted alternating sandstone (brown) and siltstone (grey) layers are very easy to distinguish.
Stop 5: Cherry Canyon Sandstone
The Cherry Canyon Formation visible at this outcrop consisted of thin tightly layered sandstone/siltstone on the uppermost section. The lower section’s layers were much thicker sandstone/siltstone bedding layers.
Cherry Canyon Sandstone/Siltstone. These are siliciclastic basinal deposits.
Stop 6: Faulted Cherry Canyon Outcrop
This outcrop was the only outcrop where we got to observe a fault mirror. Although these bedding layers were similar in composition to other areas of the Cherry Canyon Formation, there was distinct fault line with different bedding orientations to the left and right sides of the fault. The very outer left/right portion of the outcrop had bedding layer dipping at roughly 30 degrees whereas the central part of the outcrop near the fault line had bedding dipping at nearly 50 degrees. The fault gouge had created a fault mirror at the point of the fault.
Tilted layers at left side of the outcrop and fault.
Rough sketch of the outcrop.
Stop 7: Brushy Canyon/ Cherry Canyon Boundary
This outcrop was broken up into two different compositional areas. The first section that we looked at was the Frijoles site. The Frijoles site contained Quaternary aged conglomerates formed by the deposition of fan deposits during high energy/short term events. These conglomerates were what capped the Cherry Canyon sediments. Pictured below was farther down the outcrop where the actual boundary between the Cherry Canyon Formation (upper) and Brushy Canyon Formation (lower) occurred. Paleomagnetic studies have confirmed these two formations are separated by a small bed of black shale whose deposition occurred as a result of an anoxic event.
The outcrop shows the distinct boundary between the Cherry Canyon Formation (thicker bedded sandstones on the upper part of outcrop) and Brushy Canyon (thinner bedded silty sandstones on the lower part of the outcrop) separated by a shale layer (black bedding layer).
Stop 8: Bell Canyon Formation w/ Submarine Lamar Limestone Landslide
The Bell Canyon Formation is the uppermost sandstone formation you can observe as you continue into the basin. It contained large lense-like portions of carbonates that are known to be huge fragments of the Lamar Limestone (reef formation).These large fragments had been transported by submarine landslides onto previously deposited siliciclastic sediments. Some areas of the outcrop also contained Radar units within it. The top cap of the outcrop was tightly layered siliciclastic sediments.
The grey portions of the outcrop are the result of submarine landslides of the Lamar Formation (limestone/dolomite).
Stop 9: Castile Formation Evaporites
This stop was our introduction into the Castille Formation. This formation is composed of basinal evaporites. The outcrop was primarily composed of tightly layered bands of gypsum/anhydrite and halite (white to light grey in color) with intermittent laminae of dark brown colored gypsum. Considering these rocks are evaporites, for them to follow this type of formation it would suggest that the area had undergone a cycle of (1) drying through the initial evaporite process which precipitates calcite first, then gypsum, then halite; (2) wetting from some type of short lived event which reintroduced enough water to start the precipitate cycle over again while also introducing some organics (within the dark colored laminae of calcite); (3) drying after the rain event had ceased; (4) while drying the precipitation sequence began again (5) Compaction that forced the water out of the gypsum and altered it to anhydrite. Considering the high volume of layers, you can determine that this cyclic event happened over and over again across a long period of time. This Castille Formation is up to 1500 feet thick in areas so you can imagine the length of time this evaporation process has been occurring.
This specimen had fallen from the outcrop but shows the evaporite precipitation sequence as described in the text. The dark colored laminae are the calcite layers separating the gypsum/anhydrite-halite sequence.
Castille anhydrite-evaporite sequence. Image credit: Warren 2016
Stop 10: Castille Formation Evaporites
This stop was still part of the Castille formation, however, it had a great representation of the enterolithic and chicken-wire gypsum structures. These structure formed due to the re-precipitation of the anhydrite after the evaporite layers had undergone compaction turning the which turned the gypsum into anhydrite (lower thin layers). There was a distinct 6-foot-thick segment of layers that had folding occurring which suggested there was active tectonics after deposition. As you moved vertical down the outcrop from north to south the bedding layers progressively got thinner. This would be due to the compaction and re-precipitation that was occurring.
Note the lower laminae that represent the basic evaporite precipitation sequence (although the gypsum has been altered into anhydrite due to compaction) that is overlain by the chicken-wire and enterolithic anhydrite structures (lack of laminae).
Enterolithic and Chicken-wire description Image credit: after Shearman and Fuller, 1969; Warren 2016
Stop 11: Crystalline Phoenix Mine, NM
Our stop at the Selenite mine was a very cool opportunity to be able to sift through mine tailings and rock hound for selenite specimens to bring home. This was the only opportunity we had to see selenite (variety of gypsum) in the field during the trip. In addition, the sheer amount of the size of some of the sheets and columns of gypsum they had at the mine were very pleasing to see. The habit of the selenite was blocky to platy with some of the sheets being upwards of 2-3 cubic feet.
My selenite crystals from the Crystalline Phoenix Mine, TX.
This was the end of day 4.
Our trip to White Sands National Monument was mostly for enjoyment. However, once we arrived there is a great deal of geologic differences we saw in the geomorphology and tectonics of the basin area where White Sands formed in comparison to the Delaware Basin we have seen for a majority of the trip. White Sands National Monument is located in the Rio Grande Rift Zone we talked about on our first day of the trip. On our dive from El Paso to Camp Washington we drove through the southernmost area of this same rift zone heading towards the Guadalupe Mountains. On our route to White Sands we arrived into this rift zone much farther north coming through the Sacramento Mountains on the eastside.
View form the Rio Grande Overlook in the Sacramento Mountains. White Sands is visible directly behind my head.
This rift area is a product of the western plate under the eastern plate. White Sands sits on what is the Tularosa basin (graben) in-between the Sacramento and San Andreas Mountains. Unlike the open basin areas we have seen through most of the trip, the Tularosa basin is a closed basin system meaning there is none to very little outside seawater input into the basin because the basin has always been closed in by mountains. Therefore, all the water responsible for the precipitation of the most of the evaporites found in the basin are a result of the capture of rainfall by the area and surrounding mountains into the basin system. The evaporites found here are Permian in age and originate from the Yeso Formation (lagoon environment). However, the White Sands formation is much younger in age. Convergent tectonics were responsible for uplifting the gypsum deposits which allowed for winds from the southwest to transport the gypsum from the San Andreas Mountains to where they currently are now. Needless to say. These deposits are unique and quite a site to witness and explore.
Helpful diagram of the basinal graben area where White Sands Notional Monument is located and helps explain the origin of the gypsum dunes.
These beautiful gypsum dunes were easily 30-40 feet in elevation from the troughs, however, the total thickness of the gypsum beds is 300-400ft.
You can see the effects of wind action on the gypsum deposits as the secondary structure (ripples) are visible in most areas. The ripples allow you to determine the wind direction based on their formation.
These vast dunes span a total of 140 square miles.
More beautiful ripples (secondary formations) on the dune surface.
Another beautiful dune crest with ripples structures.
Some dunes exhibited small landslide type features that occurred after re-deposition of the gypsum by the wind. These crests were overloaded with sediments causing the gypsum sand to cascade down the slope and form these structures.