Integrated Litho-, Chemo- and Sequence Stratigraphy of the Ediacaran Gametrail Formation Across a Shelf-Slope Transect in the Wernecke Mountains, Yukon, Canada

Abstract

The Ediacaran Gametrail Formation of northwestern Canada chronicles the evolution of a complex carbonate ramp system in response to fluctuations in relative sea level and regional tectonic subsidence alongside exceptional global change associated with the Shuram carbon isotope excursion (CIE). Here, we use extensive outcrop exposures of the Gametrail Formation in the Wernecke Mountains of Yukon, Canada, to construct a shelf-slope transect across the Shuram CIE. Twelve stratigraphic sections of the Gametrail Formation are combined with geological mapping and a suite of geochemical analyses to develop an integrated litho-, chemo-, and sequence stratigraphic model for these strata. In the more proximal Corn/Goz Creek region, the Gametrail Formation represents a storm-dominated inner to outer ramp depositional setting, while slope depositional environments in the Nadaleen River region are dominated by hemipelagic sedimentation, turbidites, and debris flows. The magnitude of the Shuram CIE is largest in slope limestones which underwent sediment-buffered diagenesis, while the CIE is notably smaller in the inner-outer ramp dolostones which experienced fluid-buffered diagenesis. Our regional mapping identified a distinct structural panel within the shelf-slope transect that was transported ~30 km via strike-slip motion during the Mesozoic–Cenozoic Cordilleran orogeny. One location in this transported structural block contains a stromatolite reef complex with extremely negative carbon isotope values down to ~ -30‰, while the other location contains an overthickened ooid shoal complex that does not preserve the characteristic negative CIE associated with the Shuram event. These deviations from the usual expression of the Shuram CIE along the shelf-slope transect in the Wernecke Mountains, and elsewhere globally, provide useful examples for how local tectonic, stratigraphic, and/or geochemical complexities can result in unusually large or completely absent expressions of a globally recognized CIE.

Deep‐water first occurrences of Ediacara biota prior to the Shuram carbon isotope excursion in the Wernecke Mountains, Yukon, Canada

“…Previous investigations of the Wernecke Mountains have led to the identification of an Ediacaran mixed siliciclastic and carbonate succession that records the transition from inner shelf or platform to slope facies along a present-day north-to-south transect, specifically from the Goz/Corn Creek area (proximal or shallow water) to the Nadaleen River region (distal or deep water) (Busch et al, 2022(Busch et al, , 2023Macdonald et al, 2013;Moynihan et al, 2019;Pyle et al, 2004) (Figure 1). The Ediacaran succession stratigraphically overlies Marinoan glaciogenic strata of the Ice Brook Formation and the informal Ravensthroat cap carbonate (James et al, 2001;Macdonald et al, 2013Macdonald et al, , 2018Moynihan et al, 2019), which has been recently formalized as the Cliff Creek Formation (Busch et al, 2021).…”

“…Inset map: Shelf-slope transect from shallow-water facies at Goz A to offshore facies at Goz B-C, before moving into slope deposits found at Pharaoh and Olistolith Central camps in the Nadaleen River Area. Ediacaran strata in the Goz D region may have been translated into the region by later strike-slip faulting (see Busch et al, 2023). dolostone.…”

“…dolostone. In some areas, this carbonate has been identified as the Gametrail Formation (Narbonne, 2005;Pyle et al, 2004), but recent work suggested it rests gradationally upon the Sheepbed Formation and is referred to informally as the "Sheepbed carbonate" (Busch et al, 2023;Macdonald et al, 2013). At the shallowest-water Goz A section (Figure 5), the Sheepbed carbonate is capped by a subaerial karstic unconformity and overlain by interbedded shale, sandstone, and carbonate of the Nadaleen Formation (Macdonald et al, 2013) (note the Nadaleen Formation was previously referred to as the "June Beds" by Macdonald et al (2013) before its formalization by Moynihan et al (2019)).…”

“…The Nadaleen Formation is overlain by dolostone and limestone of the Gametrail Formation (Figure 2), which records the Shuram CIE (Busch et al, 2022(Busch et al, , 2023Macdonald et al, 2013;Moynihan et al, 2019). Above the Gametrail Formation, the terminal Ediacaran is recorded by the Blueflower and Risky/Algae formations (Figure 2).…”

“…The lower carbonate member is a mixed carbonatesiliciclastic interval, the middle member is exclusively siliciclastic, comprising rhythmically bedded mudstone, siltstone, and quartz arenite, and the upper member is composed of heterolithic fine-and coarse-grained siliciclastic strata. Busch et al (2023) recently proposed that the lower member of the Blueflower Formation should instead be included with the Gametrail Formation. In shallow-water settings, the top of the Rackla Group is marked by the dolostonedominated Risky Formation, while in deeper-water settings this unit is dominated by limestone and dolostone of the Algae Formation (Cecile, 2000;Moynihan et al, 2019).…”