Seismic-scale soft sediment deformation associated with subaqueous dewatering: an example from the continental shelf of the Otway Basin

Niyazi, Yakufu1, Warne, Mark2, Ierodiaconou, Daniel1

1School of Life and Environmental Sciences, Deakin University, Warrnambool, Australia; 2School of Life and Environmental Sciences, Deakin University, Burwood, Australia

Soft-sediment deformations (SSDs) are created in unconsolidated sediments and are relatively common in finer-grained depositions. Numerous natural processes can induce the SSDs, including seismicity, glaciation, thermal activity, rapid deposition etc. And the deformation often occurs rapidly, close to the surface, during or shortly after burial. The SSDs have been documented as micro-scale under the microscopes to meter-scale in the field outcrops. Here we show an example of seismic-scale SSD that might have associated with the subaqueous dewatering processes.

The Plio-Pleistocene Whalers Bluff Formation of the offshore Otway Basin is composed of mixed siliciclastic-carbonate sediments. In seismic cross-section, this formation includes an interval that is formed of alternating depressional ponds and raised ridges. This interval is shallowly buried and lies between 40–150 ms two-way travel time below the present-day seafloor. The ponds are expressed as densely packed, circular to polygonal, and in some cases, hexagonal-shaped features in time slice maps. The ponds are 200–800 m in diameter and are separated by ~20 m wide ridges. The distribution and organization of these enigmatic features closely resemble the previously documented honeycomb-like structures (HSs). In our study area, they cover an area of 760 km2, and some of them, especially those in the NE of the study area, are aligned strongly along the NW-SE trend-lines. The HSs or similar features have been documented by many studies and are related to the formation of the carbonate build-ups, polygonal faults, focused-fluid escape pipes, paleo-karsts, or soft sediment contraction accompanied by diagenetic processes. Seismic geomorphological and geospatial analysis indicate that the HSs might have been resulted from the bulk contraction of soft sediment, associated with shallow burial diagenesis processes such as subaqueous dewatering of the fine-grained successions within the Whalers Bluff Formation.


Biography

Yakup Niyazi received his M.S. in Marine Geoscience from the University of Haifa, Israel, and joined the Marine Mapping Group at Deakin University, as a PhD student in Marine Environmental Science. His main research interests include subsurface imaging, signal processing, and quantitative seismic interpretation.

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