Seafloor Depressions on the Chatham Rise, New Zealand: Their link to underlying fluid flow systems.

Abstract

In January-February 2013 an international collaboration of scientists (CHRIMP) investigated a series of seafloor depression structures on the Chatham Rise. The data used in this thesis was collected aboard the R.V. Sonne in January, 2013. This thesis re-processes a 3D seismic data set to attempt to improve image quality, and therefore make more confident interpretations. This re-processed data set has been analysed and interpreted using seismic stratigraphy and three seismic attribute methods (similarity attribute, energy attribute and spectral decomposition attribute). Seismic stratigraphy identifies groups of reflectors that represent large scale changes in depositional environments, usually across millions of years, while the attribute analysis helps refine the stratigraphic interpretations on a finer scale. The aim of interpretation is to investigate the link between a seafloor depression and an enigmatic conical feature imaged in the subsurface, as well as using the seismic interpretation regime to characterize the seafloor depression and the conical feature. The seafloor depression has been interpreted as having been deposited by a bottom current that is constrained by bathymetry (a contourite), and the conical feature as a sediment re-mobilization feature related to fluid flow. The link between these two systems is interpreted to be a group of paleo-seafloor depressions which sit atop polygonal faults. Some type of fluid is interpreted to have flowed upwards from the conical feature through a polygonal fault system, and expulsed at a paleo-seafloor, creating crater-like depressions. It is postulated that these depressions created eddies in an otherwise smooth bottom contour current, which forms the current day seafloor depression (contourite). Further research by collaborators in the CHRIMP project will help determine the type of fluid that created the paleo-depressions. This research contributes to the overall CHRIMP project by helping to characterize the link between seafloor depressions and underlying fluid flow systems on the Chatham Rise.