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Flow and Substrate Interactions of MTDs With Submarine Channels: 3-D seismic Examples From Taranaki Basin, Offshore New Zealand


Mass transport deposit (MTD) related topography affects initiation and development of submarine channels. However, exactly how the emplacement of MTDs influences the lateral migration of channels is less understood. This study uses high resolution 3-D seismic data from the offshore Taranaki basin to investigate flow interactions between two Pliocene to recent submarine channels and MTDs. Two distinct MTDs were identified and mapped to understand how substrate composition, particularly kilometre-scale megaclasts entrained within the MTDs influences flow behaviour. The older MTD overlies and conserves a channel-levee system with sinuousities in the order of 1.06 - 1.85, defined by curved inclined reflectors, identified as lateral accretion packages (LAPs). The 3.7 km long LAPs with levee height of about 60 m - 85 m reveal that the channels are preserved under blocks within the MTD and their response was controlled by the size of the blocks, flow thickness and orientation of the intervening flow. The younger MTD also overlies and mixes with a substrate containing a channel levee system that records channel avulsion processes. Our analysis reveals the gravity gliding of the 69.5 km long distal emergent slide of the MTD over an area of 181 km2 above the channel levee strata was the main mechanism behind the levee collapse that led to the avulsion of the channel, thus placing them on the same stratigraphic interval. Structural styles within the arcuate ridges observed at the distal zone of the MTD provide evidence of high friction that resulted from buttressing against the channel levee. The trend of the retraction scours on the basal shear zone of the emergent slide, together with the scoured margins of the levee supported this assumption. Understanding flow interactions between MTDs and channels is vital in understanding reservoir heterogeneity; and substrate composition controls sediment dispersal flow patterns thus affecting their capacity to act as effective petroleum plays.