Geochemical and Nd isotopic evidence for sedimentary-source changes in the Devonian miogeocline of the southern Canadian Cordillera

Abstract

Sedimentological evidence indicates that clastic sediments of the Western Canada Sedimentary Basin were derived predominantly from the north and east, an exception being the westerly sourced Sassenach Formation in the Upper Devonian. A comparison of geochemical and Sm-Nd isotopic data of the Sassenach Formation and the underlying Perdrix and Mount Hawk Formations, which have easterly sources, support a change in sedimentary provenance. The Frasnian Perdrix and Mount Hawk Formations have initial ϵ Nd values of −7 to −8.5. This range of values is higher than that of the underlying Precambrian basement and reflects a mixture of older and younger crustal detritus (Late Proterozoic to Devonian) eroded and transported from orogens in the Arctic. The overlying Famennian Sassenach Formation yields lower initial ϵ Nd values that decrease from as high as −8.5 at the base to about −11 near the top. The lower ϵ Nd values of the Sassenach Formation imply that the western crustal source of the Sassenach sediments was, on average, older than the eastern crustal sources of the underlying formations. This older western source appears to be related to uplift and reworking of older miogeosynclinal sediments in the west as a result of compression related to the Antler orogeny.