Kilometre-scale polygonal seabed depressions in the Hatton Basin, NE Atlantic Ocean: Constraints on the origin of polygonal faulting

Abstract

Polygonal faulting is a widespread phenomenon in sedimentary basins worldwide. It changes basin-scale fluid flow patterns and alters the physical properties of the sediments making it important for hydrocarbon exploration and geohazard analysis. It is generally accepted that polygonal fault patterns derive from dewatering and compaction of the host sediments, but there is debate regarding the processes that control polygonal faulting. New multibeam-bathymetry data from the Hatton Basin, NE Atlantic, show up to 10 m deep and 200–600 m wide troughs at the seabed. They connect to each other forming polygons that are several hundred metres across, i.e. of similar size as buried polygonal fault systems observed in 3D seismic data. The troughs are symmetrical and resemble elongated pockmarks. Previously unpublished high-resolution 2D seismic data from the same area show seismic disturbance zones similar to pipes observed under pockmarks elsewhere as well as faults that have all the characteristics of polygonal fault systems. The observation of the wide disturbance zones is enigmatic, as they appear to follow the polygonal seafloor pattern. The observed extent of the polygonal sediment contraction system is substantial covering almost 37,000 km 2 . We calculate that some 2600 km 3 of possibly carbon-bearing fluids have been expelled from this system and we expect that this will affect the benthic ecosystems, although so far there is only limited evidence for chemosynthetic habitats. ► Polygonal seabed depressions cover 37,000 km 2 . ► They are underlain by 2 types of deformation structures. ► Some of the seabed depressions are not linked to polygonal faults. ► Dewatering has released about 2600 km 3 of fluids to the seafloor.