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Abstract

We examine four fields of undulating sediment in the Bismarck Volcanic Arc, Papua New Guinea, to assess causal mechanisms. The possible mechanisms include deformation, episodic turbidity currents, and continuous bottom currents. Two of the fields, one off the coast of Dakataua caldera and one in Kimbe Bay, display an arcuate and irregular morphology similar to one another in multibeam imagery. In sidescan imagery, each of these fields is proximally associated with downslope scour features and other evidence of turbidity-current activity. There is no evidence of significant bottom-current activity in these regions. We suggest that these two fields were formed by a combination of extensional deformation and repeated turbidity currents, based on a quantitative analysis of their morphologies and the evidence for turbidity currents in each location. In particular, the Kimbe Bay and Dakataua fields are morphologically distinct from a field of turbidity-current sediment waves mapped nearby in Hixon Bay (Torkoro Trough field). Also in Hixon Bay, an irregular depression north of Lolobau Island that may be a slide scar appears to have provided the initial topography for a small turbidity-current sediment-wave field growing within it. Although flows that formed the sediment-wave fields in the study area are not specifically defined as mass-transport processes, the processes that preconditioned all of these field sites for subsequent sediment-wave formation clearly are. In the Dakataua and Kimbe Bay fields, the mass-transport process of sediment creep in conjunction with turbidity currents is the necessary combination of mechanisms to generate the morphology of the sediment waves observed. Likewise in the Hixon Bay fields, a slide scar exhumed by an earlier extensive mass-failure event was required to create the necessary seafloor morphology to appropriately funnel the subsequent sediment-wave-forming turbidity currents.

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