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Abstract

Copious δ13C data have been collected from Neoproterozoic successions around the world for the purpose of chemostratigraphic correlation, but few successions provide radiometric dates with which to calibrate the δ13C profiles. The Neoproterozoic succession near Pocatello, Idaho, is not particularly rich in carbonates, but it does contain important radiometric constraints not available in other sections. Four carbonate intervals are found in the succession. A thin, pink dolostone unit, located above the diamictites of the Scout Mountain Member, Pocatello Formation, records negative δ13C values and is younger than 709 Ma and older than 667 Ma. A thicker limestone unit found at the top of the Scout Mountain Member records negative δ13C values and is slightly younger than 667 Ma. The Blackrock Canyon Limestone is located above the Pocatello Formation but stratigraphically below units dated at ~ 580 Ma and contains five siliciclastic to carbonate meter-scale cycles containing oncolites and thrombolites. We interpret these as shallowing-upward parasequences. They progressively record a transition from mildly negative to mildly positive δ13C values. Finally, a thin dolostone layer located within the Caddy Canyon Quartzite records highly positive δ13C values (> 8‰) and is constrained to be older than ~ 580 Ma. The siliciclastic nature of the succession precludes continuous δ13C profiles. However, our data would suggest that the transition from negative to highly positive δ13C values occurred after 667 Ma, a conclusion that differs from other less well constrained δ13C compilations that would place the transition closer to ~ 700 Ma. In addition, the δ13C profile is similar to that from postglacial units in Death Valley to the south, and can tentatively be used to provide age constraints to this poorly dated succession.

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