δ13C Chemostratigraphy of the Neoproterozoic Succession Near Pocatello, Idaho, U.S.A.: Implications for Glacial Chronology and Regional Correlations
Published:January 01, 2007
Frank A. Corsetti, Paul K. Link, Nathaniel J. Lorentz, 2007. "δ13C Chemostratigraphy of the Neoproterozoic Succession Near Pocatello, Idaho, U.S.A.: Implications for Glacial Chronology and Regional Correlations", Proterozoic Geology of Western North America and Siberia, Paul K. Link, Reed S. Lewis
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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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Proterozoic Geology of Western North America and Siberia
This volume is a compendium of research on the Belt Supergroup. It is an outgrowth of Belt Symposium IV, held in Salmon, Idaho, in July, 2003, in conjunction with the Tobacco Root Geological Society annual field conference. Because of the geographic extent and great thickness of the Belt Supergroup, years of work have been required before conclusions are “bona fide”. The Mesoproterozoic Belt Supergroup of western Montana and adjacent areas is geologically and economically important, but it has been frustratingly hard to understand. The previous Belt Symposium volumes offer an historical view of the progress of the science of geology in the western United States. The advent of U-Pb geochronology, especially using the ion microprobe (SHRIMP) and laser-ablation ICPMS, has injected geochronometric reality into long-standing arguments about Belt stratigraphy. Several papers in this volume utilize these new tools to provide constraints on age and correlation of Belt strata (Chamberlain et al., Lewis et al., Link et al., and Doherty et al.)