A case study in the New York Drumlin Field, an investigation using microsedimentology, resulting in the refinement of a theory of drumlin formation.

The formation of drumlins remains a major enigma. It is accepted that drumlins form under active temperate ice most likely within a soft sediment deforming bed at ephemeral ‘sticky points’. These ‘sticky points’ likely lead to the causative mechanism around which sediment nucleation occurs. The critical question is under what conditions and where and how do ‘sticky spots’ form. A comparative investigation of a drumlin and mega-flute in the New York Drumlin Field, as a case study, demonstrates that rheological and sedimentological tills from these different forms are similar. It is not, therefore, rheological change alone that must account for drumlin shape and form but likely the advective subglacial basal sediment flux rate at the ice bed. The rate of sediment motion between the upper interface at the ice–sediment bed boundary, and the lower immobile sediment at depth is crucial. At the lower décollement between the mobile and immobile sediment units, within the deforming sediment package, proto-drumlin nucleation is likely to occur and develop into a streamlined form. The trigger mechanism for such a perturbation is a derivative of sediment rheology and sediment flux rate driven by the overlying ice stresses. Recent evidence from Antarctica lends credence to this new hypothesis that can be related to all drumlins formed under temperate, soft sediment deforming bed conditions. [ABSTRACT FROM AUTHOR]