GLACIAL AND GLACIOFLUVIAL DEPOSITS IN THE INTERLOBATE AREAS OF THE SCANDINAVIAN ICE-SHEET

Rapid flow within ice streams took place in a broad marginal zone of t he Scandinavian Ice Sheet during deglaciation. Ice streams and interlo bate zones have been characterised by analysis of glacial flow pattern s, and examination of sedimentary features of interlobate glacial and glaciofluvial deposits. Reconstructed glaciodynamic systems are compar ed with ice streams of modern ice sheets. Wide interstream areas of in active ice were left between some adjacent ice streams where they sepa rated during the retreat of the margin. These areas are characterised by morainic hummocks composed of both till and glaciofluvial sediment, and sections show indications of subglacial deformation. Observations from Fennoscandia suggest that these interstream areas were sites of net accumulation of glacial and glaciofluvial sediment during deglacia tion. Glaciofluvial sediment was deposited in subglacial tunnels or ca vities simultaneously with till deformation and deposition resulting f rom subglacial melting. Substantial glaciofluvial complexes were forme d in narrow interlobate joints where adjacent ice lobes coalesced. A c ase study made in southern Finland shows converging flow patterns of t wo ice lobes and intervening glaciofluvial deposits. Concentration of meltwater in interlobate zones was a consequence of ice-sheet configur ation. Thinner ice in interlobate zones caused convergence of supragla cial and subglacial drainage. The crevassed and strain-softened ice ma y also have allowed surface meltwater to penetrate down to the ice/bed interface close to the ice margin. Steep ice-velocity gradients in in terlobate zones would have increased subglacial melting rates, and thi s environment was favourable for establishment of a subglacial drainag e network and deposition of glaciofluvial sediment. (C) 1997 Elsevier Science Ltd.