Recent, arctic deltaic sedimentation: Olivier islands, Mackenzie Delta, North-West Territories, Canada

Despite a low tidal range and relatively low wave conditions, the Mackenzie Delta is not prograding seaward but rather is undergoing transgressive sho reface erosion and drowning of distributary channel mouths. In the Olivier Islands region of the Mackenzie Delta the resultant morphology consists of a network of primary and secondary channels separated by vegetated islands. New ground is formed through channel infilling and landward-directed bar a ccretion. This sedimentation is characterized by seven sedimentary facies: (1) hard, cohesive silty clay at the base of primary channels which may be related to earlier, offshore deposition; (2) ripple laminated sand beds, be lieved to be channel-fill deposits; (3) ripple laminated sand and silt, int erpreted as flood-stage subaqueous bar deposits; (4) ripple laminated or wa vy bedded sand, silt and clay, representing the abandonment phase of channe l-fill deposits and lateral subaqueous bar deposition from suspension settl ing; (5) a well sorted very fine sand bed, presumed to result from a single storm event; (6) parallel or wavy beds of rooted silt, sand and clay, inte rpreted as lower energy emergent bar deposits; and (7) parallel or wavy bed s of rooted silt and clay, believed to represent present-day subaerial bar aggradation. The distribution of sedimentary facies can be interpreted in t erms of the morphological evolution of the study area. Initial bar depositi on of facies 3 and channel deposition of facies 2 was followed by lateral a nd upstream bar sedimentation of facies 3 and 4 which culminated with the d eposition of the storm bed of facies 5. Facies 6 and 7 signify bar stabiliz ation and abandonment. Patterned ground formed by thermal contraction and preserved in sediments a s small, v-shaped sand wedges provides the most direct sedimentological ind icator of the arctic climate. However, winter ice and permafrost also gover n the stratigraphic development of interchannel and channel-mouth deposits. Ice cover confines flow at primary channel mouths, promoting the bypassing of sediments across the delta front during peak discharge in the spring. P ermafrost minimizes consolidation subsidence and accommodation in the nears hore, further enhancing sediment bypass. Storms limit the seaward extent of bar development and promote a distinctive pattern of upstream and lateral island growth, The effects of these controls are reflected in the vertical distribution of facies in the Olivier Islands. The sedimentary succession d iffers markedly from that of a low-latitude delta.