Glacial lineations in the marine environment viewed through a Palaeozoic lens

Understanding the processes at glacier beds is crucial as they regulate ice flow, basal sediment dynamics, and meltwater routing, which collectively control glacier stability and response to climate change. Fields of glacial lineations are a spatially coherent assemblage of elongate subglacial bedforms made of sediment (e.g., soft-sediment striae, flutes, drumlins, megadrumlins, and mega-scale glacial lineations) that share a common flow-parallel orientation and are interpreted to record the geometry, kinematics and dynamics of past ice flow. These assemblages are widespread in Quaternary and modern settings, in both terrestrial and marine glacial environments. However, in terrestrial environments, these lineation fields degrade rapidly after formation, and the range of structures is much more restricted. In a marine context, they have a protective veneer of glaciomarine muds and exhibit a much greater diversity. By integrating observations from exceptionally preserved Late Ordovician (ca. 445 Ma) and late Palaeozoic (ca. 300 Ma) examples in Africa and Arabia, we find that a range of scale-independent structures are characteristic of glaciomarine fields of glacial lineations. A recurrent feature is stacked lobate sediments upon which glacial lineations are superimposed, from centimetre-scale soft-sediment striae to metre-scale flutes. These features are referred to as lobate glacial lineation sets and the largest examples are synonymous with grounding zone wedges, with self-similar examples at the scale of flutes and soft-sediment striae. A new conceptual model argues for the accumulation of these deposits at a stable, tidewater glacier margin unifying micro-, meso- and mega-scale glacial lineations in a single process interpretation.