Northern Laurentian provenance for Famennian clastics of the Jasper Basin (Alberta, Canada): A Sm-Nd and U-Pb detrital zircon study

摘要

Within the carbonate-dominated Devonian succession of the Western Canada Sedimentary Basin, sandstones of the Famennian Sassenach Formation represent a sedimentological and isotopic anomaly inferred to be related to western sources uplifted during Antler tectonism. Previously reported evidence for a changing tectonic regime along western Laurentia during deposition of the Sassenach renders this unit an important potential link to shifts in source areas associated with this tectonism. We report the first set of U-Pb detrital zircon ages and new Sm-Nd whole rock data from the Sassenach Formation of the Jasper Basin in the Alberta Rocky Mountain fold-and-thrust belt. The 147Sm/144Nd ratios (0.109–0.122) and εNd values (–9.6 to –10.9) at the time of deposition are within a narrow range that overlaps with published data, confirming a post-Ordovician shift to more positive εNd values along the northern and western Laurentian margin coinciding with the introduction of more juvenile sources associated with Innuitian and Grenville sources. A previously recognized subtle negative shift in εNd values in the Sassenach relative to underlying Frasnian deposits is also confirmed, which suggests a minor contribution from more mature sources, opposite the overall post-Ordovician positive trend. Zircon ages show a wide spread (378–3506 Ma), with three broad age groups separated by a paucity of ages in the 700–900 Ma and 2100–2500 Ma ranges: (1) a narrow Paleozoic to Neoproterozoic group (378–700 Ma), (2) a broad Proterozoic group of scattered ages (900–2100 Ma), and (3) a narrow Archean group (2500–2900 Ma). Paleozoic to Neoproterozoic detrital zircon ages are absent from the western Laurentian record, and thus link the Sassenach Formation to the Arctic realm where terranes with zircons of these ages are well known. Discordance modeling suggests a consistent Pb loss in the Sassenach zircon data set (ca. 390 Ma) that coincides with the first orogenic pulse in Innuitian–Ellesmerian tectonics in the paleo-Arctic realm. Together these data suggest that the bulk of terrigenous sediment in the Jasper Basin was recycled from Ellesmerian foreland strata and subsequently transported southward along the margins of western Laurentia. Sediment transport may have been facilitated by southward-directed, shore-parallel shallow-marine currents initiated by Northern Hemisphere wind patterns.