EOLIAN-FLUVIAL INTERACTION IN THE PAGE SANDSTONE (MIDDLE JURASSIC) INSOUTH-CENTRAL UTAH, USA - A CASE-STUDY OF ERG-MARGIN PROCESSES

Channel- and lens-shaped deposits of non-eolian red sandstone are encl osed within the eolian Leche-e Member of the Page Sandstone in south-c entral Utah. Detailed analysis of lithology and geometry, and regional correlation of the red sandstone deposits suggests that the channel-s haped scours and in-filling deposits were formed by ephemeral stream p rocesses, in contrast to earlier interpretations that suggested a mari ne estuarine origin. We hypothesize that ephemeral streams transportin g volcanic debris flowed toward the north and northeast along the west ern edge of the Page erg. Local avulsion, possibly caused by eolian da mming of an adjacent drainage, led to stream flow into low areas of th e Page erg. Entrainment of loose eolian sand, combined with fluid loss via infiltration, led to a rapid increase in sediment/fluid ratio dur ing flow events, initially resulting in sandy debris flow deposition. Subsequent floods entrained less material from the underlying, more co hesive, debris flow deposits, had a lower sediment/water ratio, and he nce left deposits containing some evidence of flow turbulence. Eventua lly stream drainage avulsed again, probably back to a more northerly c ourse into the Carmel sea, fluvial deposition within the erg ceased, a nd eolian deposits covered the now intercalated fluvial complex.