Sealing potential of contourite drifts in deep-water fold and thrust belts: Examples from the Hikurangi Margin, New Zealand

Abstract

Contourite drifts form an important component of many deep-water sedimentary systems. Although their role as reservoirs, particularly along passive margins, is recognised, their sealing potential has been relatively understudied, especially along convergent margins. A range of contourite drifts has recently been recognised along the Hikurangi subduction margin, off the east coast of the North Island of New Zealand. Those occurring in shallower depths comprise giant elongate mounded and plastered drifts; they are mud-rich and blanket the crests and flanks of thrust-cored ridges. These drifts may seal reservoirs that principally comprise the turbiditic component of deformed trench-slope basin fill that was deposited adjacent to the ridges. The locations of modern hydrocarbon seeps appear to confirm the sealing potential of these drifts, which could trap significant hydrocarbon accumulations. The faults that underpin the ridges appear to act as primary charge pathways. Because the drifts are documented to drape the crests and flanks of the structural highs against which the reservoirs pinch out, there is a specific spatial and structural correspondence between seal, reservoir and charge pathways in this location. Such an association could be of broader economic significance if developed in convergent settings elsewhere.