Date of Award
Master of Science
This study focuses on the depositional transition between the Permian Cedar Mesa sand dune sea and the adjoining fluvial, lacustrine, playa and a sabkha facies. This transition provides insights into how climate and environment interacted in this unique setting where up to 300 m of eolian sands transition into evaporites. The evaporites are less common as tongues within the eolianites than previously thought and there were several environments that were observed that haven't been previously described or observed in the Cedar Mesa. The arrangement of the various units within the study area support the climate control on stratigraphy.
The intertonguing boundary between the sand of the dune sea and the muds and evaporites of the adjoining environments is exposed along the eastern edge of the Cedar Mesa plateau southern Utah. The eolian-playa transition is exposed over a 20km-long area in canyon walls, as well as in side canyons that extend into the plateau from Comb Wash. The interplay of different environments reveals how groundwater and climate influence the accumulation and diagenesis of these rocks. Abrupt ends of the eolian tongue were found to represent vegetated dune fronts, where 10- to 20-m-thick sandstones pinched out within 100 m. The paleosols covering the dunes indicate that most dunes did not form synchronously with the associated shales and were stabilized prior to burial, with concomitant early diagenesis and loss of porosity. Thick beds of mudstone and fluvial channel deposits found associated with limestones suggests a series of climate changes in the area from dry to form the dune sea to wet, thus the vegetation of the dunes and subsequent burial in mudstones. The associated channel deposits, pervasive bioturbation from roots, and lack of evaporites suggests that highly saline brines did not form adjacent to the dune sea. This indicates that stabilization by vegetation as fresh water accumulated in the porous sand was the primary control, limiting the expansion of the dune sea.
Petrographic analysis of the samples from this study area in particular tells us that sandstones that were topographically higher at the time of deposition have the higher porosity and permeability. Precipitation of carbonate cements as the water table rose as well as compaction is the cause of reduced porosity and permeability.
Received from ProQuest
Massad, Alexandra, "The Eolian-Sabkha Transition in the Permian Cedar Mesa Sandstone, SE Utah" (2013). Open Access Theses & Dissertations. 1674.