A curious feature of the Bounty Trough is that it marks the continuation of several main river features in the South Island – the "Otago Fan Complex". This is a distinct series of channels existing in the base of the trough which is an extension of the
Clutha and
Waitaki River systems. Both these rivers, especially the Clutha, are noted for their fast flow. This alone would not account for the existence of the channels, though much of their current contours was probably shaped by sediment during the ice ages. The channel system is the remnant of a
Cretaceous (failed) rift formed via ocean-floor spreading at the time when Zealandia separated from Antarctica between 130 and 85
Mya. The channels provide a major transportation system for sediments from the major rivers in the eastern South Island. At the Eastern end of the rift is the abyssal Bounty Fan. In July 2012, the
NIWA research ship mapped the area finding a structure of nine canyons ending in "a large deep apron-shaped sediment deposit in the Bounty Trough". The survey considered development of a biodiversity assessment of the area which would then support "potential environmental effects of any oil drilling, and help establish environmental guidelines specific to the area". The mapping also found "pock marks" some deep by in diameter in the margins which may indicate methane seepage. The survey could support petrochemical exploration, though, Roberts et al. found evidence of "an extensive and effective petroleum system" to be "conjectural". Both the Otago and abyssal fans, and the rift itself developed from the
Kaikoura Orogeny and were greatly accelerated after about 2.5 Ma, with the onset of global glacial/interglacial climatic cycles and the development of an icecap along the alpine region of South Island. The glacial periods contributed large amounts of sediment to the trough. Sediment is not being deposited now in the same way as it was during the glacial period. ==References==