Abstract

Multiple sedimentary structures of different scales and representative of various flow conditions were sampled from single, sand-dominated, fluvial channels in the Neoproterozoic (Ediacaran) upper member of the Stirling Quartzite and the Cambrian (Terreneuvian) middle member of the Wood Canyon Formation. Sampling was designed to determine if sorting of detrital-zircon populations by their textural properties affects detrital-zircon age spectra in fluvial sandstones. Grain sizes of the sampled host sandstones range from fine to coarse sand, and sorting ranges from moderately well to poorly sorted. Four Wood Canyon Formation samples contain detrital-zircon grains of similar size, whereas detrital zircons in samples of the Stirling Quartzite differ greatly in size between two samples. Paired Kolmogorov-Smirnov, overlap, and likeness statistical tests demonstrate that all samples from each channel are similar. Comparing size, sphericity, and roundness of detrital-zircon grains to their ages yielded no linear correlation. Sorting of sediments by their textural properties did not affect detrital-zircon age spectra in either unit. In this study, different sedimentary structures within a single fluvial channel do not control the age distribution of detrital zircons. Furthermore, the two braidplain systems (Wood Canyon Formation, Stirling Quartzite) have substantially different detrital-zircon age spectra, indicating that the fluvial environment in general is not responsible for selecting specific age populations. The dominant ca. 1.1 Ga Grenvillian peak in the middle member Wood Canyon Formation results from provenance, not sampling bias. Uplift and erosion of Grenvillian rocks along the Ouachita rift flank during the earliest Cambrian may have generated a pulse of sediment that entered a northwestward-flowing braidplain.

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