Journal Article

A fluvial origin for the Neoproterozoic Morar Group, NW Scotland; implications for Torridon-Morar Group correlation and the Grenville Orogen foreland basin

Cheer, David, Prave, Tony, Krabbendam, Maarten

2008

Overview

Precambrian sedimentary successions are difficult to date and correlate. In the Scottish Highlands, potential correlations between the thick, undeformed siliciclastic \"Torridonian\" successions in the foreland of the Caledonian Orogen and the highly deformed and metamorphosed siliciclastic Moine succession within the Caledonian Orogen have long intrigued geologists. New and detailed mapping of the Neoproterozoic Altnaharra Formation (Morar Group, lowest Moine Supergroup) in Sutherland has discovered low-strain zones exhibiting well-preserved sedimentary features. The formation comprises 3-5 km of coarse, thick-bedded psammite with abundant nested trough and planar cross-bedding bedforms, defining metre-scale channels. Palaeocurrent directions are broadly unimodal to the NNE-ENE. We interpret the Altnaharra Formation as high-energy, braided fluvial deposits. The Altnaharra Formation and the unmetamorphosed, Neoproterozoic Applecross-Aultbea formations (Torridon Group) are similar in terms of lithology, stratigraphical thickness, sedimentology, geochemistry, detrital zircon ages and stratigraphical position on Archaean basement. Depositional age constraints for both successions overlap and are coeval with late Grenvillean orogenic activity. Detrital zircons imply similar source regions from the Grenville Orogen. The Morar and Torridon groups can thus be correlated across the Caledonian Moine Thrust and are best explained as parts of a single, large-scale, orogen-parallel foreland basin to the Grenville Orogen.

• Publisher: Geological Society of London,The Geological Society of London,Geological Society,Geological Society Publishing House
• Subject: age / Altnaharra Formation / Applecross Formation / Aultbea Formation / basins / braided streams / chemical composition / clastic rocks / correlation / cross-bedding / Crystalline rocks / deformation / Earth sciences / Earth, ocean, space / Europe / Exact sciences and technology / fluvial environment / fluvial features / foreland basins / Geochemistry / Geological time / Geologists / Geology / Great Britain / Grenvillian Orogeny / Highland region Scotland / Igneous and metamorphic rocks petrology, volcanic processes, magmas / Lithology / Moine thrust zone / Moinian / Morar Group / Neoproterozoic / nesosilicates / northwestern Scotland / orthosilicates / paleocurrents / paleogeography / planar bedding structures / Plate tectonics / Precambrian / Proterozoic / provenance / River beds / sandstone / Scotland / Scottish Highlands / Sediment transport / sedimentary rocks / Sedimentary structures / Sedimentology / silicates / siliciclastics / Stratigraphy / streams / Sutherland Scotland / Torridonian / United Kingdom / upper Precambrian / Western Europe / zircon / zircon group