Geochemical investigation of a Neoproterozoic glacial unit: The Mineral Fork Formation in the Wasatch Range, Utah
The Mineral Fork Formation is an isolated unit of Neoproterozoic glaciogenic rocks in the Wasatch Range in northwestern Utah. Geochemical analyses of diamictite and mudstone samples were carried out to document its major and trace element geochemistry. Comparison of the lower and upper parts of the formation, which have been ascribed to different tectonic and sedimentological settings, revealed no striking differences, but the analyzed samples show a gradual upward increase in CaO, MgO, Fe 2 O 3 , MnO, and P 2 O 5 and a decrease in SiO 2 . TiO 2 :Al 2 O 3 ratios that suggest a provenance throughout the formation with an average composition slightly more mafic than average upper crust. The mudstones are more K rich than the diamictites. Calculation of a chemical index of alteration (CIA) is complicated by the presence of carbonate minerals. After making corrections for carbonate content, CIA values range from 65 to 70. These values are higher than those from Paleoproterozoic glaciogenic deposits. Some mudstones in the upper part of the formation are Fe rich (∼15% Fe 2 O 3 ), approaching the composition of iron formations. The ferruginous nature supports previous correlation with Fe-rich glaciogenic rocks of the Rapitan Group in the northern Canadian Cordillera. Trace elements, including rare earth elements, suggest that the materials in the Mineral Fork Formation were largely derived from a post-Archean source. Most of the widespread glaciogenic rocks of the Neoproterozoic were derived from older sedimentary materials, whereas the deposits of the earlier great glacial episode in the Paleoproterozoic contain a much higher proportion of crystalline materials.