3-D seismic study into the origin of a large seafloor depression on the Chatham Rise, New Zealand 

Tuesday, 16 December 2014
Kate Alyse Waghorn1, Ingo Andreas Pecher1, Lorna J Strachan1, Gareth James Crutchley2, Joerg Bialas3, Sudipta Sarkar3, Bryan William Davy2, Cord A Papenberg3, Stephanie Koch3, Thomas Eckardt3, Karsten Kroeger2, Paula S Rose4 and Richard B Coffin4, (1)University of Auckland, Auckland, New Zealand, (2)GNS Science-Institute of Geological and Nuclear Sciences Ltd, Lower Hutt, New Zealand, (3)GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, (4)Texas A & M University Corpus Christi, Department of Physical and Environmental Sciences, Corpus Christi, TX, United States
Vast areas of the Chatham Rise, east of New Zealand’s South Island, are covered by circular to elliptical seafloor depressions. Distribution and size of these seafloor depressions appear to be linked to bathymetry: Small depressions several hundred meters in diameter are found in a depth range of ~500-800 m while two types of larger depressions with 2-5 km and >10 km in diameter, respectively, are present in water depths of 800-1100 m.

Here we evaluate 3-D seismic reflection data acquired off the R/V Sonne in 2013 over one of the 2-5 km large depressions. We interpret that the seafloor bathymetry associated with the 2-5 km depressions was most likely created by contour current erosion and deposition. These contourite features are underlain by structures that indicate upward fluid flow, including polygonal fault networks and a conical feature that we interpret to result from sediment re-mobilization. We also discovered a set of smaller buried depressions immediately beneath the contourites. These features are directly connected to the stratigraphy containing the conical feature through sets of polygonal faults which truncate against the base of the paleo-depressions. We interpret these depressions as paleo-pockmarks resulting from fluid expulsion, presumably including gas. Based on interpretation and age correlation of a regional-scale seismic line, the paleo-pockmarks could be as old as 5.5 Ma. We suggest the resulting paleo-topography provided the initial roughness required to form mounded contourite deposits that lead to depressions in seafloor bathymetry.