Abstract

Sea cliffs at Victoria expose submarine flow tills within an ice-contact complex of flow till – outwash proglacial cones interbedded with dinoflagellate-bearing glaciomarine fine sediments. Glacial debris flow lobes (mainly flow tills) were formed by supraglacially, englacially, and basally transported sediment slumping off an ice margin grounded in the Strait of Juan de Fuca. The structures and textures reveal that lobes formed by a conveyor mechanism. In some lobes a double sorting phenomenon apparently developed involving an outer, winnowed, layer of pseudo-plastic flow around an inner core of till that was sorted by dewatering and expulsion of fines outward from the centre during flow. Structures and fabric data indicate lobe travel was gravitationally controlled down cone flanks and independent of ice movement.A depositional model for the complex proposes the ice margin produced a proglacial apron of interdigitating cones, which accumulated on the sea floor. Sediment facies variations were probably controlled by shifts in cone development along the margin: cones formed where glacial and glaciofluvial debris discharged from the ice into the sea and glaciomarine deposits accumulated from glacial flour suspended in the seawater between the cones.Although this is the first reported example of submarine flow tills, casual observations elsewhere suggest that they are common in coastal areas.

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