Geochemical constraints on the Shuram carbon isotope excursion across a shelf-slope transect in the Wernecke Mountains, Yukon, Canada

The Shuram Carbon Isotope Excursion (CIE) represents the largest δ¹³C_carb isotope excursion in Earth's history. Despite considerable research on potential driving mechanisms, there remains little consensus on the origin and diagenetic history of this carbon cycle perturbation. Here, we examine the Shuram-bearing Gametrail Formation of the Wernecke and Ogilvie Mountains of Yukon, Canada, across a shelf-slope depositional transect to elucidate the geochemical and sedimentary expression of this CIE. Over 1000 δ¹³C_carb measurements were made from ~25 detailed stratigraphic sections with selected samples being analyzed additionally for δ⁴⁴Ca, δ²⁶Mg, and major and trace element geochemistry. Along the shelf-slope transect, there is an ~10 ‰ δ¹³C_carb shift in the nadir of the Shuram CIE between proximal and distal locations, which are expressed within a diversity of sedimentary facies representing sedimentation along a distally-steepened carbonate ramp. Shallow-water sections are characterized by dolostone-dominated facies with δ¹³C_carb values reaching a nadir of ~ -5.5 ‰, with generally more enriched δ⁴⁴Ca, lower Sr/Ca, and higher Mg/Ca ratios. In contrast, slope to basin floor sections are dominantly composed of limestone facies with δ¹³C_carb data reaching nadirs of ~ -15 ‰ and more depleted δ⁴⁴Ca, higher Sr/Ca, and lower Mg/Ca ratios. These preliminary data characterize the diagenetic conditions experienced in shallow vs. deep-water carbonate settings in northwestern Laurentia and highlight a critical relationship in the nature and magnitude of the Shuram CIE and paleoenvironmental setting.