A DEPOSITIONAL MODEL FOR ROGEN MORAINE, WITH EXAMPLES FROM THE AVALON PENINSULA, NEWFOUNDLAND

Rogen moraine is explained by subglacial meltwater processes through a form analogy between moraine ridges and ripples produced on the underside of river ice. This mechanism for Rogen moraine formation is compatible with the meltwater hypothesis for drumlins. A unified explanation for Rogen moraines and drumlins is attractive and necessary because they are part of a continuum. The meltwater hypothesis is tested on Rogen moraine of the Avalon Peninsula, Newfoundland. Mapping shows that ice and meltwater flowed northeastwards from St. Mary's Bay and fanned out across the peninsula. The sedimentology of four moraine ridges and one moraine hummock favours deposition in subglacial cavities. Sediment in the ridges travelled only short distances, and there is abundant evidence of water sorting and deposition from debris flows. Bedding within ridges conforms with surface slopes, and clast fabrics relate to local morphology rather than to the regional ice-flow direction. Additional sedimentary observations from Quebec and Sweden support the meltwater hypothesis. The prevalence of local debris in Rogen moraines may reflect the importance of subglacial entrainment by freeze-on under perma-frost conditions. This may explain the geographical distribution of Rogen moraine around former ice-sheet centres.