Ancient Rocks Reveal How Glaciers Shape the Seafloor

21.08.2026

An international team of geologists has used exceptionally preserved rocks from ancient ice ages to develop a new understanding of how glaciers interact with the seafloor. Their findings, published in the journal Sedimentary Geology, offer a fresh conceptual model that provides a valuable window into modern marine ice-sheet processes that are difficult to observe directly.

The study, titled “Glacial lineations in the marine environment viewed through a Palaeozoic lens,” examines fields of glacial lineations - elongate, flow-parallel ridges and grooves left by moving ice - from Late Ordovician rocks (approximately 443 million years old) and late Palaeozoic deposits (around 300 million years old) in South Africa and Saudi Arabia.

Preserved by glaciomarine muds

Unlike terrestrial glacial landscapes, these marine examples are often protected by a covering of glaciomarine muds, preserving a richer and more diverse suite of structures. The researchers identified a recurring architecture they term “lobate glacial lineation sets”: stacked, lobe-shaped sediment packages upon which lineations are superimposed. These range from centimetre-scale soft-sediment striae to metre-scale flutes, with the largest examples corresponding to grounding-zone wedges.

Lobe-shaped sediment packages with lineations

The team proposes that these features form at stable tidewater glacier margins, where sediment is simultaneously deposited and sheared by the ice. This single process interpretation links micro-, meso- and mega-scale glacial lineations into one continuum - expanding earlier ideas about geometric relationships among larger bedforms.

“By turning to the Palaeozoic rock record, we can examine the kinds of ice-seafloor interactions that today lie beneath modern ice shelves”

“By turning to the Palaeozoic rock record, we can examine in three dimensions and at outcrop scale the kinds of ice-seafloor interactions that today lie beneath modern ice shelves or in inaccessible polar seas,” the authors note. The new model helps bridge the gap between small-scale features visible in the field and the large-scale landforms mapped by marine geophysical surveys on contemporary glaciated margins.

The research draws on detailed field observations from multiple sites across Gondwana, integrating data from the Late Ordovician and the Late Palaeozoic Ice Age. It highlights the value of ancient, well-preserved successions for interpreting processes operating at the ice-bed interface in marine settings.

Publication

An international research team lead by Daniel Le Heron from the Department of Geology, University of Vienna, compared fields of glacial lineations from Late Ordovician rocks and late Palaeozoic deposits in South Africa and Saudi Arabia. Picture: Harrisdale Farm in the northern Karoo Basin in South Africa. © Daniel Le Heron

The researchers identified a recurring architecture they term “lobate glacial lineation sets”: stacked, lobe-shaped sediment packages upon which lineations are superimposed. This photo shows a flute field at the Harrisdale Farm in South Africa, showing several slightly tapered flutes with initiating boulders at the up-glacier end. © Daniel Le Heron

They also compared their findings to modern and recent fields of glacial lineations like in the Ötztal Alps, Austria, where they have collected extensive UAV imagery of multiple ice margins, including the Vernagtferner forefield. © Daniel Le Heron

Orthophoto detail of classic flutes in the same Vernagtferner forefield with initiating boulders, morphologically analogous to those at Harrisdale Farm. © Daniel Le Heron