STROMATOLITES, MASS FLOWS, AND FLUID ESCAPE STRUCTURES, NAVAJO SANDSTONE, CAPITOL REEF NATIONAL PARK, UTAH

Five-meter-high laminated carbonate mounds occur locally on carbonate lenses within interdune sandstones exposed at three separate localities. Outcrop data suggest coeval deposition in adjacent interdune corridors. The interdune section at all three localities is overlain by a mass flow sandstone which locally is over 28 meters thick. Innumerable rip-up clasts of laminated carbonate, some over 12 meters long, are suspended within the mass flow unit. Numerous fluid-escape structures, including pillars, domes and flames up to 20 meters high, are delineated by displaced interdune carbonate beds. These spectacular structures extend upward from the interdune section to near the top of the mass flow unit. All of the interdune/mass flow outcrops appear to occur entirely within eolian sandstone. A stable high water table caused by damming of a paleo-drainage by eolian dunes may have created conditions suitable for formation of large stromatolites during interdune deposition downstream of a dam. Catastrophic failure of a large dam and draining of a lake behind it may have been responsible for the ripping-up of interdune carbonate clasts and creation of the mass flow deposit. Loading of saturated interdune sediment by the sudden arrival of a sandy mass flow may have resulted in the creation of large fluid escape structures. Without the carbonate ‘marker beds’ the mass flow unit could look like ‘massive’ or ‘contorted’ units observed elsewhere in eolian sandstones. The Capitol Reef outcrops 1) indicate that terrestrial floods and rapid changes in water table could have played a significant depositional role in ancient eolian environments, and 2) may suggest a means toward regional correlation within the Navajo Sandstone.