Holocene evolution of the nearshore sand wedge,South Otago continental shelf, New Zealand

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Abstract
The 85 km long, inner–middle continental shelf off South Otago, is mantled by a near-shore sand wedge. High resolution seismic profiles show that this feature is most developed in Moly-neux Bay, where a combination of sheltered water and abundant sediment supply, chiefly from the Clutha River, have encouraged deposition of up to 34 m of Holocene sediment. The wedge appears to have evolved in two main stages. In the early Holocene, a lower wedge, W3, formed against a shoreline which is tentatively correlated with a –27 to –24 m stillstand between 9600 and 8800 years ago. W3 initially prograded across the floor of Molyneux Bay to the open shelf, where currents redirected sediment northeastwards. Wedge accumulation diminished with resumption of the Holocene transgression. When sea level stabilised at its present position 6500 years ago, the second stage commenced with deposition of modern sand, W1, over the lower wedge. Development was again influenced by shelf currents which controlled wedge morphology and redistributed sand 60 km along the middle shelf and 190 km along the littoral zone. The lower wedge appears to have accumulated faster than its modern counterpart, presumably in response to enhanced sediment supply accompanying major changes in the early Holocene climate and oceanography.