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Department of Geography, Queen’s University, Kingston, Canada K7L 3N6
Sources of rafted sediment include glacial, colluvial, fluvial, aeolian and littoral settings. Processes of incorporation and rafting include active incorporation by freezing and passive loading of icebergs and sea ice, and rafting by vegetation, principally marine algae. Passively loaded sediments, being loose on the ice surface, are more easily lost from the raft and are more likely to form deposits of more than one particle at a time. The effectiveness of passive loading depends on sea ice being in contact with the shore in the spring, when colluvial and fluvial processes are most active, and during winter when aeolian processes occur. Actively incorporated sediment becomes concentrated on the surface of the raft by melting. Other factors that control distribution of rafted sediments include the strength and stability of the raft, its rate of deterioration, its ability to leave the source area, and its movement at sea.
Sediment released from the ice is deposited as single particles (referred to as a ‘drop’), agglomerations of more than one particle (‘dump’), frozen aggregates, and deposits from the melting of sediment-laden ice in contact with the sea floor. Characteristics that have been used to distinguish the mode of rafting include grain size, sorting, shape, surface features (especially striations), fabric, fauna associated with the environment of origin, distance of transport, and water depth. The most reliable in assessing origin from an iceberg is probably the presence of striations, although none is conclusive, and interpretations must be made cautiously.
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  References Geological Society, London, Memoirs, 1997; 17: 477 - 514. [PDF]
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