LATERAL CONTROLS ON BASIN SCALE CARBON ISOTOPIC EXCURSIONS IN EDIACARAN MARINE CARBONATES OF THE CANADIAN ROCKIES

Values of δ13C measured from marine carbonates from the Ediacaran Period display tremendous variability. Many of these variations are considered excursions and often are interpreted as reflective of changes in either oceanic dissolved inorganic carbon (DIC) values, or local, post-depositional changes- collectively known as “diagenesis”. Ediacaran carbonates of the Old Fort Point Formation in the Canadian Rockies outcropping in Jasper and Lake Louise, Alberta, display values ranging from -6‰ to -12‰. This isotopic range is observed to be stratigraphically coherent with low point-to-point variability. To explore lateral variability in δ13C values, we measured and sampled several stratigraphic sections in the Canadian Rockies, separated by approximately 250 km. To test the hypothesis of a diagenetic origin, prevalent carbonate-clast breccias found in numerous stratigraphic sections were sampled to conduct ‘isotope conglomerate tests’ (ICTs) to determine the relative timing of acquisition of the δ13C values measured. Geochemical results indicate that this excursion (down to values of -12‰) is present across the Canadian Rockies. Further, clasts within interbedded breccias that may have formed by eroding through this strata, contain the full range of δ13C variability found in entire sections. Together these observations suggest a primary origin of isotopic values. To consider primary, non-diagenetic processes occurring in an ancient shallow water system that could have led to these low values, we developed a one dimensional linear advective-diffusion carbonate sedimentation and isotopic tracer model. Model runs suggest that lateral variability in primary δ13C values of carbonate sediment in shallow basin settings can lead to stratigraphically coeval isotopic excursions that nevertheless do not require secular evolution in δ13C values of oceanic DIC. This study will advance the understanding of how carbon isotopic variability is controlled and expressed within the convoluted and highly variable geochemical record of the Ediacaran.