CYCLING THROUGH THE GRAND CANYON: GEOCHEMICAL AND MAGNETIC VARIABILITY OF PARASEQUENCES IN THE TONIAN CHUAR GROUP DISTINGUISH BETWEEN A LACUSTRINE AND MARINE SETTING

Cyclic facies of the Tonian Chuar Group have been proposed to record glacioeustasy and local hydroclimate oscillation in response to orbital forcing. This interpretation suggests high latitude ice may have existed ca. 30 Myr prior to the Sturtian Snowball glaciation ca. 717 Ma, and relies on the interpretation that the Chuar Group was deposited in a marine basin. However, potential paleosols and abundant exposure surfaces suggest that much of the Chuar Group may have been deposited in a lacustrine environment. Here we present bulk sediment environmental magnetics and elemental compositions with 25 cm sample spacing over 100 m of the lower Carbon Canyon Member of the Galeros Formation, Chuar Group. Proxies for terrigenous flux, clay abundance, chemical weathering, carbonate abundance, and grain size suggest that red shales and carbonates were deposited during arid climates coupled with shallow water depths. Additionally, these shallow red shales contain hematite and can be identified through their coercivity and increased saturation magnetization. Conversely, wetter climates coupled with deeper water depths permitted increases of clay abundance and decreases in grain size. Correlation between total iron and magnetic susceptibility suggests paramagnetic minerals, e.g. iron-bearing clays, are an important contributor to total iron values. Symmetrical proxy behavior around carbonates suggests sinusoidal, not sawtooth, water depth variability, which is inconsistent with the interpretation of glacioeustasy driving cyclical facies changes. Additionally, the repetitive wet-dry cycles represented by lithological changes occur over > 5 m scales, which based on age constraints would be equivalent to > 100,000 year time-scales. Therefore, the lower Carbon Canyon Member of the Chuar Group was likely deposited in a lacustrine environment where water depth variability would have been driven by local hydrology.