Abstract Many of the pebbles in the late Precambrian Torridonian arkose (Applecross Formation) of northwest Scotland cannot be traced to the underlying Lewisian basement complex. Pebbles regarded as exotic include quartz-tourmaline rock, tourmaline-aplite, quartz-fuch- site schist, pure and iron-rich metaquartzite, fine-grained igneous rocks comparable with porphyritic rhyolite and acid tuffs, and a large variety of orthoquartzite and chert. The Applecross Formation was deposited as large alluvial fans which spread out from the west. These arkosic sediments, with the exception of the exotic pebbles, probably were derived from a basement complex similar to that of northwest Scotland. The approximate maximum area of the drainage basin of the Torridonian alluvial fans has been estimated by comparison with those of modern alluvial fans. The Torridonian drainage basin, as plotted on Bullard et al.’s (1965, Fig. 7) reconstruction of the North Atlantic region prior to continental drift, is within the continental margins between Scotland and southeast Greenland. A study of the literature concerning the Precambrian rocks of southeast Greenland indicates that several of the Torridonian exotic pebble types can be matched with Precambrian rocks exposed in that region.

Abstract Fluvial point-bar deposits are described from the c. 1 Ga Diabaig Formation, representing some of the most compelling architectural evidence of planform sinuosity recognized in pre-vegetation sedimentary strata to date. The stratigraphical architecture of the deposits indicates different planform transformations in response to meander-bend expansion and downstream migration. Point-bar architectural motifs are locally abundant in the unit and this is attributed to elevated amounts of mud-calibre cohesive sediment. Mud afforded landscape stability that, together with limited stream power, was sufficient to corral sediment into single-thread, sinuous channels. Significant volumes of fine-grained sediment were encouraged to accumulate by the local basin setting of several topographically confined endorheic depressions. These conditions ceased once the hydrologically closed valleys were filled, with the overlying sandstone-dominated Applecross Formation subsequently deposited by low-sinuosity, braided rivers that bypassed fine-grained sediment oceanward. Other endorheic basins conducive to the formation of depositional meanders should be expected to have been relatively widespread on pre-vegetation Earth, though many individually limited in size, confined by their inherited topographies. Depositional architectures representative of sinuous channel planforms remain scarce within more extensive, externally drained basins.

Abstract The Stoer, Sleat and Torridon groups lie unconformably on Palaeoproterozoic Lewisian metamorphic rocks. They contain organic carbon microfossils claimed to be non-marine and to include eukaryotes. We consider the evidence for terrestrial interpretations from each formation of the Torridonian Supergroup. The range of sedimentary structures and the boron content of illite led us to the overall conclusion that, based on the currently available evidence, the Torridonian Supergroup was probably entirely non-marine. Evidence for terrestrial life in these rocks comes from microbially induced sedimentary structures, including wrinkle structures with reticulate and elephant skin fabrics. Organic remains and microscopic carbonaceous compressions mostly reported from phosphates in the grey shales of the Stoer, Aultbea and Applecross formations are dominated by sphaeromorph acritarchs. The Diabaig phosphatic lagerstätte includes three-dimensional preservation of eukaryotic and prokaryotic organisms, providing remarkable insights into non-marine life around 1 billion years ago. Supplementary material: Taxonomy of Torridon Group microfossils from thin sections of phosphatic material (adapted from Battison 2012) is available at https://doi.org/10.6084/m9.figshare.c.3522753