Depositional Environment of White Rim Sandstone (Permian), Canyonlands National Park, Utah: ABSTRACT

Abstract

The White Rim Sandstone of Leonardian age forms prominent topographic benches west of the Colorado River in Canyonlands National Park. Its origin has been interpreted as eolian or marginal marine by various authors without specific evidence other than the large-scale cross-stratification which is generally conspicuous. A detailed study of the gross geometry, cross-stratification, ripple marks, trace fossils, and facies relations of the sandstone revealed a subaqueous environment of deposition which was probably sub-littoral marine. The formation contains numerous offshore bars that were constructed by surf and longshore currents moving from the northwest as shown by bar trends and cross-stratification analyses. Numerous small bars with 10-20 feet of relief occur in a northwesterly trending swarm northeast of Elaterite basin near the Green River. A larger elongate bar with 200 feet of relief extends in an arcuate northwesterly direction for about 10 miles through Elaterite basin. Excellent exposures of sedimentary structures reveal that the original geometric configuration of the bar is preserved. Th sandstone grades abruptly into fine-grained lagoonal redbeds just east of the Elaterite bar, forming a stratigraphic oil trap that has been exposed by Recent erosion. The shallow-water bar apparently was constructed on the nose of the Monument upwarp which was mildly positive, providing shoal conditions at the time of sedimentation. Pre-Triassic (Hoskinnini?) redbeds were deposited across the White Rim Sandstone, draping over the bars preserved at its upper surface. Subsequent erosion prior to Moenkopi (Triassic) sedimentation produced local angular unconformities along the margins of the bars. End_of_Article - Last_Page 453------------