INTEGRATED LITHO-, CHEMO- AND SEQUENCE-STRATIGRAPHY OF THE EDIACARAN GAMETRAIL FORMATION ACROSS A SHELF-SLOPE TRANSECT IN THE WERNECKE MOUNTAINS, YUKON, CANADA

The Ediacaran Shuram carbon isotope excursion (CIE) represents the largest negative δ¹³C_carb excursion in Earth’s history. Despite ongoing debate about the origin and nature of this event, its isotopic expression has been widely used to correlate Ediacaran strata worldwide. Here, we examine Shuram-bearing Gametrail Formation across a shelf-slope transect in the Wernecke Mountains of Yukon, Canada, to elucidate the stratigraphic expression of this CIE. Thirteen detailed stratigraphic sections were measured of the Gametrail Formation across an ~100-km-long transect with m-scale sampling of carbonate for various isotopic analyses. Over 1000 δ¹³C_carb measurements have been made with selected samples being analyzed for δ^44/40Ca, δ²⁶Mg, and major/trace element geochemistry. The Gametrail Formation increases in thickness by more than four-fold from the most proximal to the most distal locations along the shelf-slope transect. Multiple well-defined transgressive-regressive (T-R) sequences within the shelf system pass to cryptic conformable contacts within the slope. Along this depth transect, there is an ~10‰ δ¹³C_carb shift in the nadir of the Shuram CIE, which is expressed within a diversity of sedimentary facies reflecting sedimentation along a distally steepened carbonate ramp. Inner ramp sections are characterized by dolostone facies with δ¹³C_carb values reaching a nadir of -5.5‰, with more enriched δ^44/40Ca and lower Sr/Ca. In contrast, slope sections are composed of limestone facies with δ¹³C_carb data reaching a nadir of -15‰ and more depleted δ⁴⁴Ca and higher Sr/Ca values. These data highlight a critical depth-dependent relationship in the nature and magnitude of the Shuram CIE.