Comparing and Contrasting Slump-Related Mass Transport Deposits and Depositional Wavefields Offshore Papua New Guinea

Gary Hoffman¹, D. Orange², N. Driscoll³, and B. Applegate^4
1 University of California, Santa Cruz, CA
² AOA Geophysics, Inc, Moss Landing, CA
³ Scripps Institute of Oceanography, UCSD, La Jolla, CA
⁴ Hawaii Mapping Research Group, Honolulu, HI

Seafloor images (multibeam, side scan) and high-resolution sub-bottom profiles from the Bismarck Sea along the north coast of Papua New Guinea show both slump-related mass transport deposits (MTDs) and fields of upslope migrating bedforms. In the literature, the origin of features characterized by “undulating” or “wavy” morphology have been interpreted as deformational, depositional, or hybrid (both), with a fair amount of controversy surrounding the interpretations. In the Bismarck Sea, both deformational and depositional features are present in the same region (but spatially separated), are imaged with the same acquisition systems, and therefore provide a valuable opportunity to compare and contrast deformational MTDs and deep water sedimentary wavefields. Both the depositional bedform fields and the slump-related MTDs occur in areas up to 40 km long by 20 km wide, with individual bedform / block heights reaching ~50 m and wavelengths of 500m to 1km. Slopes typically average ~1 degree, but are locally as high as 10 degrees.

To compare and contrast features of deformational (MTD) versus depositional origin, we evaluated the wavelength, height, and asymmetry from the multibeam bathymetry, the sidescan backscatter imagery, and the detailed geometry of the blocks/bedforms with high-resolution chirp sub-bottom profiles. Two regions of undulating or wavy seafloor are interpreted as deformational in origin (slumps), with associated mass transport deposits. A deformational origin is supported by the map view distribution of headscarp, sidewall scarps, evacuation zone, slide block geometry, and run-out in map view. In cross-section, the well-imaged headscarp breakaway zone, and the headwall-footwall geometries across the faults separating individual MTD blocks, clearly support a deformational origin. In parts of the slide deposit, however, we note that some of the slide blocks experienced a post-deformational period of sediment accumulation, leading to an interaction of early deformation and late sedimentation.