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Controls on Submarine Channel Type and Distribution in Complex Tectonic Settings: Examples From the Hikurangi Subduction Margin, New Zealand


Controls on Submarine Channel Type and Distribution in Complex Tectonic Settings: Examples from the Hikurangi Subduction Margin, New Zealand

Deepwater channel systems function as conduits transferring sediment across submarine slopes to the deep-sea. Numerous factors have been identified to influence the inception and evolution of channels, including external (e.g. tectonics) and local controls (e.g. levee failures). Here we examine subduction-wedge traversing systems, where multiple styles of channel occur within, connecting and beyond the discrete sub-basins of the accretionary margin. Variations in channel type and location constrain sediment distribution, resulting reservoir architecture and thus the prospectivity of deepwater basins.

Integration of outcrop data from the exhumed portion of the wedge, bathymetric studies of the seafloor and analysis of 2D and 3D seismic data from across the margin allows recognition of four types of channel system: 1) Relatively short (<10 km), typically meters deep by tens of meters wide features, with heterolithic fill, isolated within mudstone at sub-basin margins and interpreted to be largely bypass-dominated slope channels acting as feeding conduits to sub-basins; 2) Intra sub-basin, axial features, tens of kilometres long, tens of meters thick and up to 1 km wide, with sandstone rich fill and laterally bounded by irregular thin-bedded turbidites; they are interpreted as sub-basin axial channel-levee systems; 3) Major erosion surfaces tens to hundreds of meters deep and kilometres wide filled with amalgamated sandstones and conglomerates, situated on sub-basin margins and interpreted as transverse, sub-basin linking systems; 4) Trench axial channels, kilometres wide by hundreds of meters thick, with bounding levees kilometres wide, running for hundreds of kilometres along the subduction trench. The fundamental control on channel distribution, connectivity and architecture is evolving seafloor structures. However, factors such as interactions with mass-transport deposits are seen to influence channel avulsions, stacking patterns and bypass potential to outboard areas of the slope and abyssal-plain.

Channels may form reservoirs in their own right and may also bypass material to otherwise sediment-starved accommodation. Understanding how channel initiation and development dictate the location and character of these conduits through time is therefore essential to locate reservoir quality sediments, thereby de-risking frontier deep-water exploration areas.