Subaerial terminoglacial fans III: overview of sedimentary characteristicsand depositional model

A general model is presented for the small type of fans (not to be confused with sandurs) that develop subaerially in the zone immediately before an i ce front. These fans have in common with other fans that a proximal, a midd le and a distal subenvironment - with distinctly different sedimentary faci es - can be distinguished. The characteristics of these fans differ in seve ral respects, however, from those formed under other conditions, particular ly by the high proportion of mass-flow deposits in the proximal part, by th e relative scarcity of fine particles in the middle fan, and by the relativ ely uniform character of the sediments in the distal fan. The special character of this type of fan is ascribed to the interaction of a continuously changing distance between the ice front and the fan (as a r esult of alternating phases of ice advance and ice retreat), its position t hat may be surrounded by ice for a large part, and the irregular supply of debris-laden meltwater that comes sometimes even in the form of more or les s catastrophic floods. Due to the fact that terminoglacial fans have a good preservation potential only during phases of ice retreat, these fas tend to show a slight fining- upward tendency. The slope of terminoglacial fans tends to be more gentle ( rarely over 2-5 degrees) than that of fans formed under different condition s.