Abstract

The Middle Jurassic Carmel Formation and Page Sandstone were deposited in two major transgressive-regressive cycles of the Jurassic Western Interior seaway. Nonterrigenous deposition on a shallow somewhat restricted shelf was interrupted several times by the influx of terrigenous clastics. This cyclic pattern resulted in complex facies distribution across southern Utah and northern Arizona. During peak carbonate deposition at maximum transgression, biomicrite was deposited in offshore, open shelf-slope marine conditions. Eastward, oosparite and pelmicrite were deposited in oolitic shoal and restricted shelf environments, respectively, and dolomicrite formed at the shoreline by algal and sabkha processes. Inland, gypsiferous mudstone was deposited by supratidal and sabkha processes. Eolian dunes were locally present farther inland.

During peak clastic deposition, sandstone and mudstone were deposited in subtidal environments where local sand waves formed. The laminated and cross-bedded sandstone facies was deposited to the east as beach-shoreface deposits. Inland, the cross-bedded sandstone facies formed a vast sand sea complex.

Within the major dual cycles were numerous smaller transgressive and regressive cycles. Eight time lines have been constructed within these cycles throughout the study area. Identification of facies patterns along each of these approximate time lines allows construction of facies and paleogeographic maps that document changing environmental conditions within the Middle Jurassic of Utah.