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Back to list of UTIG presentations at AAPG's 2003 Annual Meeting Three-dimensional Architecture of Shelf-building Sediment Drifts in the Offshore Canterbury Basin, New ZealandHongbo Lu1, Craig Fulthorpe2, and Paul Mann2. A grid of high-resolution, multichannel seismic profiles from the offshore Canterbury Basin, New Zealand, reveal that at least eleven large (up to 1000 m thick, >50 km long, along-strike, and 20 km wide, down dip) elongate sediment drifts developed within the lower Miocene to Recent shelf-slope sediment prism. The drifts overlie a condensed section of late Oligocene limestones and cover an area of ~5000 km2. The drifts were initiated in water depths of 300-750 m, by a northward-flowing contour current. The drifts exhibit mounded morphologies with channel-like moats along their landward flanks. Erosion of the landward banks of moats creates prominent diachronous unconformities. Internal architecture defines two end members of elongate drift, described as simple and complex. Early simple drifts are small (<400 m thick). Drift thickness increased as the shelf aggraded and the locus of drift development migrated northeastward through time. Late simple drifts are therefore larger (up to 1000 m thick). These late drifts are subdivided into three parts (base, core, and crest) based on seismic facies, which form in response to progressive confinement of current flow within the moat. Complex drifts may be multi-crested or multistage. Multi-crested drifts form in response to rapid lateral shifts in position of the moat, perhaps associated with relative sea-level change, modulated by paleoslope inclination and orientation. Such drifts, together with the observation that several drifts were commonly active simultaneously, indicate that flow patterns were complex and involved multiple pathways. Multistage drifts comprise superposed subdrifts, whose retrogradational and progradational stacking patterns indicate fluctuations in the rate of sediment supply.
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