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Dimensions of Fluvial Geobodies in the Middle Williams Fork Formation (Late Cretaceous), Main Canyon, Colorado

Harper, Ericka 1; Cole, Rex D.1; Pranter, Matthew J.2
1 Department of Physical and Environmental Sciences, Mesa State College, Grand Junction, CO.
2 Department of Geological Sciences, University of Colorado, Boulder, CO.

The north face of Main Canyon, located in the southwest Piceance Basin near Palisade, Colorado, has spectacular exposures of fluvial sandstone geobodies that are analogs for gas-producing reservoir elements in the Piceance Basin. The canyon face (azimuth = 105 deg) is approximately 3.5 miles long, 700 to 800 ft high, and is orientated oblique the general paleocurrent direction (azimuth mean = 40 deg). The top of the study interval is approximately 1,200 ft above the Rollins Member of the Iles Formation, and sandstone abundance ranges between 45 and 75 % (i.e., moderate to high net-to-gross). Sedimentologic data suggest that the geobodies were deposited by low-sinuosity to braided fluvial systems that produced numerous amalgamated channel-form elements. Grain size ranges from fine to lower coarse, sorting from moderate to poor, and small- to medium-scale cross-stratification is common. Geobodies are isolated by flood-plain mudrock, consisting of gray-green, fissile siltstone and sandy siltstone. Apparent-width and maximum-thickness data were determined for 56 geobodies using ground-based photomosaics, oblique aerial photos, vertical orthophotos, and aerial LiDAR data. Maximum thickness values range from 28 to 200 ft, with a mean of 65 ft and a standard deviation of 35 ft. Apparent-width values range from 109 to 5,205 ft, with a mean and standard deviation of 1,085 and 944 ft, respectively. Dimensions of the geobodies increase upward through the study interval. This data set provides input for future stratigraphic modeling of the middle Williams Fork Formation from the perspective of vertical and lateral connectivity of reservoir elements plus well-spacing issues.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009