Grenville Foreland basin sedimentation in Scotland: structure, stratigraphy and sedimentology of the early Neoproterozoic Torridon and Morar group sequences

• Main Authors: Krabbendam, Maarten, Bonsor, Helen, Prave, Tony, Strachan, Rob
• Format: Text
• Language: English
• Published: 2011
• Subjects: Earth Sciences; Arctic; Canada; Greenland; Norway; Svalbard; East Greenland
• Online Access: http://nora.nerc.ac.uk/id/eprint/14121/; https://nora.nerc.ac.uk/id/eprint/14121/1/EGU2011-2477_mkrab_Morar.pdf; http://meetings.copernicus.org/egu2011/

The Grenville Orogen was pivotal in the amalgamation of the Rodinia Supercontinent and resulted from the continent-continent collision between Baltica-Laurentia and Amazonia. Detrital zircon geochronology has shown a number of earliest Neoproterozoic (c. 1000 – 960 Ma) successions in Arctic Canada, East Greenland, Svalbard and Norway to be sourced from the Grenville Orogen. One of the most complete and most proximal of those occurs in Scotland, represented by the Torridon and (metamorphosed) Morar groups. Structural restoration of later Caledonian and Knoydartian deformation shows that the preserved part of this foreland basin measured at least 250 x 250 km with a minimal stratigraphic thickness of 6-9 km. Following several years of structural, stratigraphic and sedimentological research, the following depositional evolution can now be reconstructed: 1) an initial progradational episode marked by coarse, fluvial braidplain mollasse-type sediments deposited directly on basement and orogen-parallel (eastward) palaeocurrents (Applecross Fm of the Torridon Gp; Lower Altnaharra Fm of the Morar Gp); 2) a switch to orogen-normal palaoecurrents (northward) concomitant with a transgression from fluvial (Aultbea Fm of the Torridon Gp; Upper Altnaharra Fm of the Morar Gp) to tidally influenced distal fluvial and shallowmarine sand deposits (lower and upper Glascarnoch Fm, resp., of the Morar Gp) and then to finer-grained, deeper-marine sediments (Vaich Pelite Fm of the Morar Gp); and 3) a brief return to fluvial-deltaic deposition before resuming the shallow-marine transgressive trend (contained in the Crom Fm of the Morar Gp) into very fine-grained deep-marine deposits (Dibiedale Fm of the Morar Gp). Given the tectonic stability of the underlying Archaean cratonic basement and the absence of evidence for rifting, we interpret this depositional pattern to be primarily caused by fluctuations in sediment flux due to changes in the uplift rate within the Grenville Orogen. Both Scottish and Canadian Grenvillean eclogites ...