Spec. Publ. Int. Ass. Sediment, 17 (1993), 63-76

I.P. MARTINI¹ J.K. KWONG² and S. SADURA¹

1Department of Land Resource Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada
²Dames and Moore Ltd, 1144-10th Ave, Suite 200, Honolulu, HI 96816, USA

The Albany River is a typical meandering to anastomosing, non-glacial stream, which crosses vast, unconfined peatlands and is affected annually by ice drives, jams and ice rafting. The amount of sediment rafted by ice is large during spring breakup (approximately 3.5 x 104 t), but it is a single annual event, and the rafted load is less than 1% of the total yearly suspended load of the river. However, this material is deposited preferentially in specific parts of the channels and on non-forested overbank areas, where characteristic deposits develop. The rafted sediment consists of material placed in the ice in a variety of ways: (i) suspended load material is emplaced partly during freezeup, but mostly during breakup when flooding occurs; (ii) pebbles are lifted from the river bed by anchor ice; and (iii) bank material slumped onto the ice during spring thawing. Released rafted sediments have diagnostic features which are retained where not reworked by water flow. These features consist of patchy silt drapes over grassy banks, lenses of unsorted coarse sand and pebbles in fine overbank deposits, lenses of poorly sorted gravel and isolated pebbles and boulders strewn on levees and the treeless deltaic floodplain. Furthermore, the gravel deposits have a polymictic composition and usually contain angular pebbles of local carbonate and reworked, rounded cobbles and boulders of crystalline glacial erratics. All these sedimentary features constitute environmentally diagnostic 'textural inversions' and should be recognizable in ancient geological sequences. They and the presence of thick, widespread organic layers (peat, coals) should allow ready distinction between cold, non-glacial streams and the more typically braided glacio-fluvial deposits which may also show well defined rhythmic sedimentation where a suitable mixture of gravel and sand exists.