Insights into the Devonian–Carboniferous transition and Hangenberg Event from δ13Ccarb and 87Sr/86Sr chemostratigraphy of shallow platform carbonate strata of northwestern Colorado.

Paired chemostratigraphic and biostratigraphic data suggest that the Devonian–Carboniferous boundary and the Hangen‐ berg extinction event are recorded in the Coffee Pot Member of the Dyer Formation of the White River uplift region of northwestern Colorado. The Hangenberg isotopic excursion interval occurs in biostratigraphically depauperate shallow plat‐ form micritic dolostone and limestone representing the aculeatus–?ultimus–kockeli? Zone. The Hangenberg interval strata have δ¹³C^carb values up to 7.69‰, and locally contain ooids, stromatolites, and other microbial structures. In three sections, there is a short-lived > 4‰ “pre-Hangenberg” positive excursion that is associated with the presence of detrital dolomite siltstone. The main Hangenberg isotopic signature exists in overlying strata, and is replicated in four different sections of the Dyer Formation across an area ~300 km². In each section, the excursion interval is preceded by, and in one location is inter‐ rupted by, evidence of meteoric diagenesis and/or emergence characterized by macroscopic dissolution features and pro‐ nounced negative δ¹³C^carb values (to ca. -6‰). Conodont ⁸⁷Sr/⁸⁶Sr ratios through the Dyer Formation dip to nearly 0.708 during the onset of the Hangenberg Event, consistent with the brachiopod based ⁸⁷Sr/⁸⁶Sr nadir from the same interval in Missouri, France, and Germany. The least-radiogenic trendline through the Dyer ⁸⁷Sr/⁸⁶Sr record matches the global mini‐ mum ⁸⁷Sr/⁸⁶Sr trendline through the Famennian–Tournaisian transition and infills several gaps in the global record. [ABSTRACT FROM AUTHOR]