PROVENANCE OF THE MUDDY CREEK FORMATION NEAR MESQUITE NEVADA AND ITS BEARING on THE PALEO-COLORADO RIVER HYPOTHESIS

We conducted provenance studies (conglomerate, petrographic and detrital zircon (DZ) analyses combined with paleoflow studies) in fluvial strata in three areas of the exposed upper portion of the Muddy Creek Formation (MCF) and inset Pliocene units near Mesquite Nevada. The first study area was within the Beaver Dam Wash upstream of where it merges with the modern Virgin River. The second area included the modern Virgin River and outcrops near Littlefield, AZ that are located immediately downstream of where the Virgin River and Beaver Dam Wash merge. Our third area was within the MCF from Mesquite southeastward towards Overton.

Paleocurrent data indicate that flow directions were to the south in the Beaver Dam Wash sections, were to the SSW at Littlefield and were to the SW in sections southwest of Mesquite (i.e., they mimic modern drainage patterns). Provenance data from Beaver Dam (conglomerates, petrography) reveal a significant volcanic component throughout the section and DZ data reveal populations as young as 18-20Ma. We interpret this section as having received significant input from the Miocene Caliente Caldera Complex which sits north of the study area. Petrographic and DZ data from the Virgin River and Littlefield sections are very similar and reveal a much more complex provenance that contains some Caliente Caldera derived material mixed with a significant component that can be tied to the Colorado Plateau. The provenance at Flat Top Mesa near Mesquite mimics the results from Beaver Dam Wash but conglomerate results from uppermost portions of the sections further to the southwest increasingly match results seen at Littlefield and sandstones further to the south become progressively less dominated by volcaniclastic components. Petrographic results vary significantly based on the location of each section but are unchanging within a specific section. However, DZ ages in the MCF change significantly upsection with increasing numbers of younger zircons in the youngest strata. These results suggest that previous interpretations which were based mainly on uppermost MCF data do not necessarily rule out deposition by a paleo-Colorado River.