Sedimentology and stratigraphy of a terminal fluvial fan system : the Permian Organ Rock Formation, South East Utah

• Main Author: Cain, Stephen
• Published: Keele University 2009
• Subjects: 551.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.518336

The fluvial Organ Rock Formation, which forms part of the Pennsylvanian-Permian Cutler Group of the Paradox foreland basin, is exposed across much of SE Utah and adjoining parts of northern Arizona and represents a wedge of coarse-grained fluvial strata that progressively fines south-westwards (distally) away from its source area, the Uncompahgre Uplift. By the time of onset of Organ Rock deposition (Leonardian/Artins kian), the Paradox basin was in an overfilled state, resulting in the progradation of a 100 m-thick wedge of fluvial strata across a wide part of the basin floor. These deposits record a downstream transition from a proximal fluvial system that was dominated by in-channel sedimentation in which evidence for repeated nodal avulsions is common, through a medial zone in which channels lay within belts that were subject to a variety of lateral accretion, avulsion and anabranching processes, to a distal zone where evidence for in-channel sedimentation is less abundant and in which sheet flood and aeolian dune elements are dominant. This research presents the first detailed sedimentological and stratigraphic analysis of the Organ Rock Formation. Gross-scale facies distributions and sedimentary architecture have been analysed using a comprehensive set of regionally and more locally distributed sedimentary logs acquired throughout the outcrop belt of the Organ Rock Formation within SE Utah. These data have formed the basis for more detailed architectu ral analyses enabling the development of a suite of two-dimensional and three-dimensional depositional models that account for the detailed and complex vertical and lateral facies relationships observed throughout the Organ Rock Formation. It is likely that the spatial and temporal evolution of the Organ Rock fluvial system was controlled by a combination of intrinsic and extrinsic processes, which acted at a range of scales and which are represented by a hierarchy of cyclicity observed at outcrop.