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3D seismic-geomorphology and seismic-sedimentology of marine bedforms

As the oceanographic understanding of internal waves is advanced, their role in sedimentological processes has recently become the focus of increasing attention. This study analyses a large section of modern seafloor in a region with a pronounced internal wave regime and explores different possible interpretations for the origin of observed bedforms. To this end, the seafloor geomorphology and shallow-subsurface information provided by a giant (>12.500 km²) industrial 3D seismic-reflection survey imaging the outer shelf and upper slope of the Browse Basin region on the North West Shelf of Australia is examined. The most prominent seismic-geomorphological features of the modern seafloor are submarine terrace escarpments, scarps of active faults, incised valleys and canyons as well as restricted areas of surface-seismic distortion interpreted as sites of gravity-driven mass wasting. Besides these kilometre-scale features it was also possible to document smaller sedimentary bedforms including sediment waves up to 10 m high. These occur in water depths below 250 m in extensive fields located dominantly at the foot of submerged terraces, along the scarps of modern faults, and at the transition between the outer shelf and the continental slope. Another bedform that commonly characterises the more planar regions of the outer shelf are elongate NW-SE-oriented furrows and ridges. The formation of sediment waves and longitudinal furrows and ridges requires flow velocities between 0.3-1.5 m/s, depending on the local sediment composition. In the studied setting, these velocities can be best explained as being generated by internal waves or internal tides. In addition to the detection of individual 3D seismic-geomorphological features of the modern seafloor, it was also possible to map buried sediment waves in the seismic dataset down to ca. 500 ms (TWT) below the seafloor. This is - to our knowledge - the first 3D seismic observation of buried, kilometre-scale sediment wave fields, which documents a certain potential for the preservation of such bedforms in the sedimentary record.

Associated researchers: Johannes Belde, Stefan Back, Lars Reuning