Depositional Facies and Potential Bounding Surfaces Along an Erg Axis to Erg Margin Transect, Permian Cedar Mesa Sandstone, Utah

Abstract

The Permian (Wolfcampian) Cedar Mesa sandstone in southeastern Utah is a ~300m thick erg system spanning 8000km2. This study characterizes the vertical and lateral variation in depositional facies of the Cedar Mesa sandstone along 7 measured sections spanning 80km through southeast Utah. Analysis of outcrop data indicates that the Cedar Mesa is comprised of two primary facies associations. Aeolian facies are dominated by large-scale trough cross-bedded or wind-rippled sandstones with minor finer-grained interdune deposits. Fluvial facies consist of small (< 0.5m) planar cross-bedded, current rippled and bioturbated sandstones and pedogenically-altered mudrocks. The vertical transition from fluvial to eolian facies is sharp and in outcrop facies are often continuous on the order of 600 meters. Occasionally fluvial facies occupy aeolian interdunes as well as interfinger with dune deposits, suggesting coeval deposition. Towards the erg margin, Aeolian deposits are relatively thin and fluvial facies comprise nearly 40% of the section indicating a complex depositional environment with prolonged fluvial influence. In the erg axis, fluvial facies become increasingly discontinuous and less abundant while aeolian facies become thicker with well-developed deflationary surfaces. The relative abundance of hiatal surfaces (deflationary or flood-dominated) decreases from erg margin to erg axis. This suggests at least some of the fluvial incursions along the erg margin are localized and likely had little impact on deposition within the erg axis. Across the Cedar Mesa erg, deposits tend to be progressively dominated by fluvial or wet interdune facies indicating a trend towards a relatively wetter environment through time.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017