Palaeogeographic implications of heavy mineral and detrital zircon provenance of Devonian sediments in the North Atlantic region

As a result of the collapse of the overthickened Caledonian crust, several extensional intramontane basins developed in the North Atlantic region in the aftermath of the Caledonian orogeny. Thick successions of siliciclastic sediments formed within those continental basins during the Late Silurian to Early Carboniferous recording the late stages of the Caledonian orogeny. Previous studies have suggested that these basins were interconnected sub-basins similar to the basins in the Basin and Range Region of the United States.

Here we present new detrital heavy mineral and zircon geochronology data of sedimentary successions from NE Scotland, East Greenland and SW Norway to reconstruct their provenance. Understanding the provenance of the sediments formed in this area plays an important role in the reconstruction of the regional Devonian palaeogeography. This study also demonstrates the importance of using a combined approach to the regional correlation of sedimentary successions.

Previous studies on the sediments of the Clair Basin, west of the Shetland Isles, led to a subdivision of the sediments into three groups based on the relative abundance of ‘Caledonian’, Proterozoic and Archaean zircons and the relative abundance of detrital heavy minerals. The Archaean dominated ‘Group 2’ was derived from the local Archaean metamorphic basement, whereas the other groups seem to have more distal source areas. Sediments from the Orcadian Basin show age spectra dominated by Proterozoic zircons, similar to ‘Group 1’ in the Clair Basin, indicating either a common source area for these two sub-basins or different source areas containing basement of a similar age. Detrital zircon age spectra from sediments from Canning Land and Wegener Halvø in East Greenland and the Devonian basins of SW Norway are also dominated by Proterozoic zircons. However, some differences in age spectra indicate a similar but probably not the same source area for the sediments from NE Scotland and East Greenland and a local source for the Devonian sediments of SW Norway.

Assemblages of detrital heavy minerals indicate that various degrees of post-depositional diagenesis and metamorphism have influenced the Devonian sedimentary successions in the North Atlantic area. For this reason, ratios of heavy minerals with similar hydrodynamic and diagenetic behaviour have been used for this study. Both heavy mineral assemblages and heavy mineral ratios seem to reflect the influence of local sources within the different sub-basins.

The combined detrital zircon and heavy mineral data suggests that rather long rivers were draining the basement of the East Greenland Caledonides, transporting material as far as NE Scotland. The Devonian basins of the Norwegian Caledonides on the other hand, seem to have had no or only a limited connection with the basins to the east.