129-28 Unfreezing Snowball Earth: The Basal Ediacaran Cap Carbonate Record in Northern Utah and Southeastern Idaho, USA

Abstract:

The cap-carbonate records in northern Utah and southeastern Idaho provide a better understanding of the duration and style of Marinoan deglaciation and how it relates to global climate change and animal evolution. 

This research evaluates sedimentary and stratigraphic features within new and formerly discovered cap carbonates that overlie Cryogenian glacial successions in the region. We conducted field work, detrital-zircon geochronology, and carbon-isotope analyses at nine Utah locations, within and around the Great Salt Lake and the Huntsville area, in the northeastern Wasatch Mountains. Although both Sturtian and Marinoan strata are recognized, only the Marinoan strata are capped by conspicuous carbonate facies.

Basal Ediacaran cap carbonates were previously described in the Pocatello Formation in southeast Idaho. This cap succession is a siliciclastic-bearing, buff- to pale-pink dolostone unit and includes features such as turbidities, bar forms, swaley cross beds, plane beds, and sedimentary breccias with an overall trend indicating decreasing accommodation space (e.g., post-glacial isostatic rebound). The overlying strata are argillaceous with rare interbeds of rippled micrite and rare cm-scale aragonite fans indicating post-glacial transgression. C-isotope values from the cap sections of Idaho range from -6 to -3 per mil. Detrital zircons from quartz sandstone within the cap carbonate at Scout Mountain, SE Idaho yield a U-Pb CA-ID-TIMS age suggesting basal Ediacaran deposition. 

Cap carbonates in northern Utah show similar features to those in SE Idaho. The Salt Lake cap sections exhibit peloids and ‘giant wave ripples’. The cap carbonate on Antelope Island is a structural outlier and contains tubestone, sheet cracks, and cryptalgal laminations. Most Utah caps overlie and/or are interbedded with silicilastics. Stable-carbon isotope values also range from -6 to -3 per mil. The collective cap carbonate record in Utah and Idaho indicate dynamic changes in accommodation space and an interplay with siliciclastic sedimentation suggesting a more protracted deglaciation.

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