Dune architecture and diagenetic history of a twenty-meter eolian succession, Cedar Mesa Sandstone, SE Utah

David Moore Tatum, University of Texas at El Paso

Abstract

The Permian Cedar Mesa Sandstone of southeastern Utah represents an eolian succession that exhibits complex spatial variation in dune architecture and diagenetic history. The Cedar Mesa Sandstone was deposited as a dune sea with a fluvial environment to the northeast, a marine environment to the west and playa environment to the southeast. ^ Paleowind measurements, surface elevations and permeability characterized the dune architecture of a twenty-meter eolian succession. Results confirm that flood (bypass) surfaces and supersurfaces extend from the northeast into the Cedar Mesa erg margin. Supersurfaces bound the studied interval and represent an apparent transgression of the erg. Flood surfaces bound eolian packages that have complex internal geometries. Flood and supersurfaces have 4 to 8 m of relief, some of which results from soft sediment deformation during deposition of the unit. Complex dune geometries could not be traced in the lower and thinner flood surface bounded intervals because the units were thinner than the migrating bedforms. ^ In the thicker middle unit, a large paleotopographic high or draa was delineated by climbing and descending trough cross beds. The trough cross beds are inferred to be deposits of migrating out of phase barchan dunes. These were migrating to the southeast, obliquely up and down the flanks of the north-northeast trending draa. Down climbing dunes reflect the eastward migration of the draa. ^ Petrographic results illustrate complex diagenesis during burial and after compaction. Research identifies five diagenetic facies. Facies represent eight stages of the diagenetic history of the studied interval. Fossil fragments found below supersurfaces represent an apparent transgression of the erg. The red coloration originated in the desert environment at the time of deposition. The white units, bleached by acidic reducing fluids after Laramide uplift of the plateau presumably represent exhumed hydrocarbon reservoirs or migration paths that created late secondary porosity. ^ This thesis for the first time documents widespread presence of fossil fragments along the supersurfaces. These surfaces are inferred to be maximum flooding surfaces in the transgressive part of a high-frequency stratigraphic sequence. This is the first time that the Permian non-marine facies have been linked to a sequence stratigraphic framework. ^ Earlier depositional models for the studied 20-m thick interval did not reflect flood (bypass) surfaces. The dunes and associated wet interdunes were assumed to climb, reflecting a relatively continuous and contemporaneous aggradation and rising water table. This study suggests that the water table did not keep up with eolian aggradation and was not important in preserving the upper parts of the unit. ^ The complex geometries exposed in the study area also imply a much more complex preserved stratigraphy, with large undulations, oblique to the main dune migration. This type of feature can be imaged seismically and can help enhance oil exploration and recovery.^

Subject Area

Geology

Recommended Citation

Tatum, David Moore, "Dune architecture and diagenetic history of a twenty-meter eolian succession, Cedar Mesa Sandstone, SE Utah" (2007). ETD Collection for University of Texas, El Paso. AAI1444128.
http://digitalcommons.utep.edu/dissertations/AAI1444128

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