Abstract

Late Wolfcampian marine transgression in the Paradox basin resulted in deposition of the littoral marine Cedar Mesa Sandstone in the vicinity of Canyonlands National Park, Utah. Fluvial sediment derived from the Uncompahgre Mountains to the east was quickly redistributed by waves and longshore currents. Foreshore laminated sandstones and crossbedded longshore bar deposits formed in high-energy zones near shore, while silty mudstones were deposited from suspension offshore. Southeasterly-directed winds, which were responsible for active longshore currents, reworked shoreline sand into back-beach eolian dunes.

Sea-level fluctuations, possibly induced by intermittent uplift of the Uncompahgre Mountains and/or subsidence of the Paradox basin, are represented by a 15 km wide zone in which shallow marine and fluvial sediments directly interfinger. By Leonardian time, a major marine regression resulted in progradation of nonmarine redbeds of the Organ Rock Formation into the Canyonlands area. This major regressional phase is reflected in the Cedar Mesa in Canyonlands by a vertical change from marine facies in the lower part of the section to predominantly eolian dunes in the upper part.