Early basin development of the Dalradian Supergroup

The Dalradian Supergroup represents an important phase of Neoproterozoic sedimentation on the eastern margin of Laurentia, yet its early depositional history and palaeogeographical context remain incompletely understood. This study integrates lithostratigraphic, sedimentological and detrital zircon U–Pb data to refine correlations between the early Dalradian Supergroup of mainland Scotland and the Colonsay and Bowmore groups of the Inner Hebrides. Multidimensional scaling of detrital zircon age spectra, coupled with lithological and geochemical similarities, supports a threefold subdivision of the Colonsay Group that parallels the Glenshirra Group and the Corrieyairack and Glen Spean subgroups of the Grampian Group of the mainland Dalradian. Coarse fluvial–deltaic and alluvial fan deposits in the initial basin infill of the Colonsay Group yield unimodal Paleoproterozoic zircon populations dominated by local Makkovik–Ketilidian–Rhinnian basement sources, whereas younger shallow-marine sediments show increasing Grenville-aged input. These trends, mirrored in the Glenshirra and Grampian Group succession, suggest a shared tectonic regime and sediment routing system. The Bowmore Group, although tectonostratigraphically distinct, displays detrital zircon signatures comparable with the upper part of the Glen Spean Subgroup and early Appin Group of the Dalradian Supergroup. Collectively, the data support early Dalradian sedimentation within a foreland basin setting, potentially initiated during the mid-Tonian Knoydartian Orogeny. Shifts in the detrital zircon spectra are interpreted here to record a transition from proximal to more distal sediment sourcing in a flysch setting, the progressive infilling of topographic lows and the expansion of a molasse apron across eastern Laurentia.