This study will examine isotopic and geochemical records preserved in the laminae of pedogenic carbonate coatings in soils in the Capitol Reef--Boulder Mountain region of the Colorado Plateau. First, the team will check for preservation of stratigraphic order in the laminae of coatings by microscopy, high-resolution X-ray mapping, and Th/U age dating. Coatings that preserve an intact stratigraphy will be micro-sampled for detailed Th/U age transects, stable isotope analysis, and trace element analysis. The team will compare well-dated profiles of stable isotope shifts from coatings collected at various depths below the soil-air interface to reconstruct the timing and magnitude of ecological and climatological changes that occurred over the measured time interval. This study will evaluate the problem of discontinuities in the pendant record which could be related to climate change on orbital time scales. Timing and mechanisms of carbonate formation will be evaluated with in situ soil moisture, respiration, and temperature measurements.
Stable isotope analysis of modern and fossil pedogenic carbonate has advanced the understanding of continental paleoclimatology, as well as documenting worldwide ecological shifts. Most stable isotope studies of pedogenic carbonate have sampled soil carbonate at a fairly coarse resolution; only a few have studied the stable isotope record of soil carbonate coatings of the large clasts within a soil horizon. This work will test thick, well-laminated, pedogenic carbonate coatings for records of a meaningful paleoclimate signal in terms of their stable isotope record (13C/12C and 18O/16O) when coatings preserve an intact stratigraphy. If true, and there is some preliminary Th/U and stable isotope data that supports this, then the world's deserts may contain a vast and untapped quantitative archive of past continental climactic and ecological variability.
This project is a collaborative effort between the University of Utah and Western State Colorado University. It will enhance education opportunities for both a research institution and an undergraduate institution, and its results will be incorporated into an international course, taught each year at the University of Utah, using stable isotopes as tracers in anthropology, ecology, forensics, geology, hydrology, oceanography, and zoology.
