Infilling history of a Neoproterozoic intracratonic basin: Nd isotope provenance studies of the Uinta Mountain Group, Western United States

Abstract

Neodymium isotope and selected trace element concentration data were obtained from 27 samples of shales and arkosic sandstones comprising the Neoproterozoic Uinta Mountain Group (UMG) in north-eastern Utah and northwestern Colorado to determine the provenance of siliciclastic detritus deposited in this region and to reconstruct aspects of the Proterozoic geologic history of the southern margin of the Archean Wyoming Province. In the east lobe of the Uinta Mountains, coarse-grained components of the Jesse Ewing Canyon Formation, the oldest recognized formation of the UMG, have measured ϵ Nd values of −23 to −28 and were most probably derived from Archean basement of the Wyoming Province to the north. Fine-grained sediment in the southern portions of the Jesse Ewing Canyon Formation and shales and quartz arenites from overlying undifferentiated UMG all contain at least a component of detritus derived from Proterozoic crust. In the west lobe, the oldest members of the UMG (the Red Castle Lake, Gilbert Peak and Moosehorn Lake Formations) and arkosic arenite comprising the northern portions of the overlying Mount Watson Formation were also derived exclusively from Archean sources. However, as in the east lobe, the more mature sandstones that dominate the southern sections of the Mount Watson Formation have isotopic compositions that require a significant Proterozoic-crust derived detrital component. Our data support a model in which sedimentary rocks with an Archean provenance represent the preserved remnants of alluvial fans marking the northern margin of the basin in which the UMG was deposited. A source for these sediments within the Archean Wyoming Province is consistent with the high light rare-earth element (LREE) and Th abundances of finegrained, low ϵ Nd, sedimentary rocks, given that Late Archean granitic rocks within the Wyoming province have similar trace element characteristics. Sediments with Proterozoic components in both the east and west lobes were apparently deposited from a fluvial system that transported sediment along the basin axis. The Proterozoic detrital component in these sediments originated either through direct erosion of the Colorado Province in the Neoproterozoic, or through erosion of ‘mixed’ Archean and Proterozoic crust located to the east of the UMG basin that originally formed during the Paleoproterozoic accretion of the Colorado Province to the southern margin of the Wyoming craton.