The pre-depositional history of the Applecross Formation, Northwest Highlands, Scotland

[摘要] The provenance of Applecross Formation sedimentary rocks (Torridon Group, Northwest Scotland) is a topic of significant debate owing to difficulties in clearly correlating various datasets for the region (detrital mineral studies, sedimentology, and palinspastic restorations) to create an accepted palaeogeographic reconstruction. This study aims to elucidate the source area of Applecross sedimentary rocks and modes of deposition and transportation.LA-ICP-MS 206Pb/238U dating of detrital zircon samples from various stratigraphic levels within the Applecross Formation type area is utilised to assess variations in the source over time. Sampling is spread through ~2000m of stratigraphy, along a ~15km outcrop parallel transect between Applecross and Loch Kishorn. Data reduction is undertaken using Iolite data reduction software.U-Pb detrital zircon peaks of Mesoproterozoic (1280-1520Ma) and late Palaeoproterozoic (1680-1980Ma) age are dominant throughout the Applecross Formation. Minor early Palaeoproterozoic (2191-2265Ma) and Archean components up to 3346±43Ma are present. These data are in broad agreement with detrital zircon data from elsewhere in the Applecross Formation presented by Rainbird, Hamilton and Young (2001) and Krabbendam et al. (2017), suggesting a uniform input of well mixed sediment from a single source. Terranes in the foreland basin of the Grenville Orogen are favoured as source areas, with transport in an orogen axial foreland trunk system. Detrital Zircon U-Pb geochronology is combined with sedimentological context to determine depositional style. Deposition is interpreted to occur in a large scale distributive system similar to the Okavango Delta, Botswana, with unconfinement occurring during an extensional phase of the Grenville Orogen associated with rotation of Baltica relative to Laurentia at the time of deposition (see Rivers, 1997; Cawood et al., 2007). This proposal correlates known detrital mineral and sedimentological datasets. Further work is required to support the model; additional detrital zircon datasets are required to confirm the validity of a single sediment input. Further evidence for localised extension in the Applecross region is required to substantiate unconfinement of an established foreland trunk river system.

[发布机构] University:University of Glasgow;Department:School of Geographical and Earth Sciences

[关键词] Detrital, zircon, u-pb, la-icp-ms, geochronology, fluvial, provenance, Scotland, Applecross, Torridon Group, Torridonian, sedimentology, planform, depositional style.