Faculty Mentor: Larry Coats (Geography, University of Utah)

Project Background

During the Late Wisconsin, alpine glaciers and pluvial lakes were present in the Great Basin. In Smith Creek Canyon in the northern Snake Range Lake Bonneville reached 3-4 km below the entrance of the canyon (Emslie and Mead, 2023). While mountain glaciers reached as low as 29000 meters a large gap remained between the lake and glaciers. This gap would have been home to different biotic communities, some of these containing Pleistocene fauna that no longer exist at this site.

Ladder Cave is located on the northern face of Smith Creek Canyon. It sits at 2060 meters in elevation within steep east-west limestone cliffs. It has two entrances, one on south side and one on the north side. The north entrance is surrounded by xeric pinyon juniper woodlands as well as an abundance of desert plants. Water runs in the canyon throughout the year, however the level of flow has varied over time. During the late Pleistocene if would have been a very different environment. For example, there was much more effective moisture than we have today, either because of lower temperatures or higher precipitation, this glacial environment would have supported different floral communities than present today.

From previous work we know bristlecone pine, Engelmann spruce, and the Rocky Mountain juniper were present at lower elevations and growing in the valleys below the cave (Thompson and Mead 1982). Initially, with Lake Bonneville at its high stand, this vegetation would have surrounded the lakeshore. After the Bonneville Flood the basin would have transformed into marshes and wetlands. Finally, in the Holocene, modern day aridity would eventually set in, although there were cooler phases with increased precipitation earlier, and dry periods with intense droughts later (Wriston 2008).

The purpose of this study is to detect ecosystem changes, specifically floral changes, that are revealed by the study of cave sediments from Ladder Cave. Because of the abundance of floral macro- and micro-fossils in these sediments, reconstruction of the late-glacial to Holocene transition will be possible at a detail never attained before.

Methods

Ladder Cave Test Pit 4 was excavated in 2023. This test pit reached a depth of 140 cm, with and radiocarbon analysis confirming that the ages range from 50,000 yr BP to present. Once sediment was collected from the cave it was brought back to the lab for processing. The sediment was first washed and dried. After sediment was washed, it was transferred into a bag to be picked. Sediment from Ladder Cave has preserved several types of insects, macrofossils, and microfauna. The tools needed in the picking process are small tweezers, a microscope, a metal dish, and a petri dish. It is a tedious process where you use these tweezers to pick up every fossil one by one. Once picking was finished, the sediment was sorted into vials. Finally, the fossils were identified and sent for radiocarbon dating.

After everything has been sorted and identified, I made a C2 graph to display the data. C2 is a program made specifically for displaying, analyzing, and visualizing paleoclimatic data. The C2 graph displays seven different species from levels 1-7. The graph uses numbers to show abundance. One means there is little material present, 2 being moderate, and 3 being the species is very abundant.

Results/C2 graph explanation

The C2 graph (figure 1) displays different species who each thrive in unique conditions. The presence of Pinus longavea (bristlecone pine) reflects cooler and wet conditions. Celtis reticulata grows in the bottomlands of rocky canyons and prefers dry conditions. Acer glabrum (rocky mountain maple) is absent in level seven, and becomes spare in 4-6, 1-2 and is more prevalent in level 3. The change in occurrence means there is variability in precipitation. Pinus monophylla (pinyon pine) in present in levels 5-7 as well as 1-2. It becomes absent in levels 3-4. Pinyon pine typically grows in association with juniper and prefers dry rocky slopes. Juniperus osteosperma (Utah juniper) is present in all levels and is most abundant in 1,2, and 5. Juniper prefers dry conditions with hot dry summers, and warm wet winters. The increase in the upper levels indicates a shift toward drier conditions. Ribes montigenum (mountain gooseberry) has little variation level to level. It is however less abundant in the upper levels and prefers dry conditions, but it will grow along streams and washes. Jamesia americana (cliff bush) is present in all seven levels with an increase in abundance in levels 3-5. Like its name, cliff bush prefers sandstone cliffs as well as a wetter climate.

Conclusions

With the conclusion of this study, there has been an increased abundance of data from a variety of floral macro- and micro- fossils. During the late Pleistocene there was more effective moisture due to lower temperatures or higher precipitation. This is reflected by the presence of species that prefer these environments like bristlecone pine and cliff bush. Past climate regimes allowed for mesic and xeric communities to occur in the same environments. The next steps for this project would be preparing for publication.

Bibliography

Emslie, S. D., & Meltzer, D. J. (2019). Late Quaternary vertebrates from the Upper Gunnison Basin, Colorado, and small-mammal community resilience to climate change since the last glacial maximum. Quaternary Research, 92(2), 388-407.

Mead, J. I., Emslie, S. D., & Meltzer, D. J. (2023). Late Pleistocene herpetofauna from two high-elevation caves in the Upper Gunnison Basin, Colorado. Western North American Naturalist, 83(3), 413-426.

Reheis, M. (1999). Highest pluvial-lake shorelines and Pleistocene climate of the western Great Basin. Quaternary research, 52(2), 196-205.

Wriston, T. “Great Basin Archaeology During the Middle Holocene: a Reflection of Environmental Change.” AGU Fall Meeting Abstracts. Vol. 2008. 2008.