Stratigraphy, provenance and tectonic setting of the Lumsden Dam and Bluestone Quarry formations (Lower Ordovician), Halifax Group, Nova Scotia, Canada

Résumé

Cambrian to Ordovician metamorphosed clastic sedimentary rocks of the Meguma terrane have no correlatives elsewhere in Atlantic Canada but are similar to successions in North Wales. In the Meguma terrane, the Cambrian Goldenville Group, dominated by sandstone, is overlain by the Halifax Group, consisting mainly of fine-grained slate and siltstone. Within the Halifax Group widespread Furongian black slate units are overlain by greyer units with rare Early Ordovician fossils, assigned to the laterally equivalent Bear River, Feltzen, Bluestone Quarry, Lumsden Dam and Glen Brook formations. The type section of the Bluestone Quarry Formation, here defined, is on Halifax Peninsula, where four constituent members are recognized; the type section of the Lumsden Dam Formation is here defined in the Lumsden Dam region near Wolfville. Detrital zircons extracted from a sample of the Lumsden Dam Formation show a range of ages similar to those displayed by the underlying Goldenville Group, including abundant Neoproterozoic zircon representing Avalonian or Pan-African sources, and a prominent group of peaks between 1.95 and 2.2 Ga, probably representing sources in West Africa. A sample from the Glen Brook Formation east of Halifax shows a similar distribution. In contrast to the correlative Welsh successions, no influx of Mesoproterozoic zircon is seen in Early Ordovician samples, suggesting that, if the two basins were in close proximity in the Cambrian, they had diverged by the Early Ordovician, possibly as a result of strike-slip motion along the margin of Gondwana.