CONODONT AGE CONTROL ON WESTWARD SHEDDING OF LIMESTONE COBBLES FROM THE INCIPIENT UNCOMPAHGRE UPLIFT, SALT VALLEY ANTICLINE, NE PARADOX BASIN, UTAH

A distinctive three meter-thick conglomerate bed comprised chiefly of rounded limestone cobbles and boulders is exposed in the northern part of the Salt Valley salt anticline north of Moab, Utah. This near-vertical bed forms part of a 30 meter-thick block of likewise steeply dipping shallow-marine and prodeltaic siltstone and shale beds that were rafted upward into their current position by salt diapirism. Workers in the late 1920’s and early 1930’s determined that constituent boulders were derived from Mississippian-age source beds on the basis of marine invertebrates. Conodont recoveries from limestone cobbles confirm the Mississippian age diagnosis. More germane to the question of the evolution of the Uncompahgre Uplift are abundant conodont elements from fine-grain strata bracketing the Uncompahgre-sourced conglomerate bed. Four prodeltaic shale beds located 11.8, 10.1, 8.5, and 3 meters below, and one newly discovered spiculitic packstone bed located 13.5 meters above the limestone conglomerate contain abundant Idiognathodus- and Neognathodus-dominated conodont faunas. Ranges of constituent morphotypes are limited to the early Desmonesian stage indicating that incipient uplift of the southwestern Uncompahgre Uplift and perhaps subdivision of the Eagle-Paradox interbasin connection began during early Medial Pennsylvanian time. This is somewhat earlier than models based upon interpretation of seismic lines that traverse Salt Valley.