Upper carboniferous to upper permian 13C-enriched primary carbonates in the sverdrup basin, Canadian arctic: Comparisons to coeval Western North American Ocean Margins

Abstract

Carbon isotopes analyses performed on more than 250 limestone samples from thirteen late Paleozoic autochthonous formations of western and Arctic Canada demonstrate that: (1) For a given locality, the δ 13C-values are uniform and there is no temporal increase in δ 13C during the whole Late Carboniferous (Pennsylvanian), Early Permian and basal Late Permian (latest Permian strata being absent). (2) There is a well-defined latitudinal trend showing that for any specific time interval, extremely high δ 13C-values are encountered in the Sverdrup Basin ( +5 to + 7%), intermediate but still high values in northern Yukon Territory ( +3 to +5%), and low values in east-central and southeastern British Columbia ( +1 to +3%). A model is proposed whereby oceanic stagnation and thermohaline stratification prevailed in the Sverdrup Basin. As a result, large amounts of 12C-enriched organic matter were preserved in central parts of the basin. As the organic matter accumulated, residual dissolved carbonate species became enriched in 13C. Additional enrichment was also promoted by the escape of CO, from evaporating brines following intermittent closures of the Sverdrup Basin early during the Late Carboniferous. Since the Sverdrup sea was connected to the Paleopacific ocean during most of its history, it acted as a source of 13C-enriched surface waters which were then spread southward by wind-driven surficial currents. With this model, the trend of decreasing δ 13C in a southerly direction is explained by increasing dilution with waters of the Paleopacific along the western margin of North America.