Facies characteristics of a proglacial turbiditic sand-lobe at Svalbard

Abstract

A shallow marine turbiditic lobe, inferred to be associated with an ice-contact delta, was deposited during the last glaciation (Weichselian) at Svalbard, the Norwegian Arctic. The postglacially raised sandy lobe is exposed in a 200-m-long river-section and exhibits six units that reflect an early phase of glaciomarine mud deposition followed by three episodes dominated by deposition from sandy turbidity currents. The lobe is characterized by a complex pattern of turbidite-filled erosional features, from thin scour-fills, reflecting a highly mobile flow pattern, to stacked chute-fill deposits showing confined flow. The sandy turbidites show ‘rhythmic’ deposition of massive to graded laminae deposited from suspension, alternating with faint laminae or ripple cross-lamination, deposited from tractional transport. Semi-continuous turbidity currents are thought to have been generated by retrogressive slumping of ice-proximal well-sorted sandy deposits on the delta front and slope. The lateral and vertical changes of lithofacies within the sandy lobe, are mainly attributed to normal mechanisms of turbiditic lobe growth, with only minor effect from synsedimentary glacier terminus movement and minor changes in the meltwater outflow position. This detailed mapping of facies changes allows a fairly accurate reconstruction of the axis of the former discharge outlet.