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The Marriage of Eolian Rock Properties and Deformation of the Nugget Formation; Anschutz Ranch East Field: Northeast Utah and Southwest Wyoming

Keele, Dustin, James P. Evans, and W. David Liddel
Utah State University, Logan, UT

     The Nugget Formation in the Anschutz Ranch East field, northeast Utah and southwest Wyoming, provides an exceptional example of how eolian rock properties have a considerable influence on the style of structural deformation. Both new and existing subsurface data were integrated for an overall characterization of sedimentologic and diagenetic heterogeneities, which demonstrate relationships with different styles of structural compartmentalization in reservoirs. The Anschutz Ranch East field is a large asymmetric anticlinal trap in the Utah-Wyoming thrust belt. Three cores were analyzed in order to investigate brittle deformation in eolian facies; dune, toe of a dune, and interdune. Selected cores are located along the back limb of the main structure and are nearly perpendicular to the fold axis. Each eolian facies appears to have an associated style of deformation that generally occurs within this tectonic setting. Within the dune facies, deformation bands are the most common style of deformation, unless a fault is present. When faults are present open fractures and breccia occur. In the toe of a dune facies, open fractures are more prevalent; however deformation bands are still very frequent. The primary style of brittle deformation observed in interdune facies is breccias and closed fractures. This relationship between facies and rheology also correlates with porosity. These results support a hypothesis that high porosity rocks tend to be weaker and develop deformation bands, while in low porosity rocks, rock strength is greater and will deform brittlely.


AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah