Seismic Studies of Paleo-Pockmarks on the Chatham Rise, New Zealand

Abstract:

This study investigates buried pockmark features on the Chatham Rise through the analysis and interpretation of 2D seismic and Parasound data. The main objectives of this research are to establish what caused the formation of buried pockmarks on the Chatham Rise and to determine when the pockmarks were formed. The study area is located on the Western Chatham Rise, near the Canterbury Shelf off the East Coast of New Zealand. The pockmark fields were revealed through multibeam bathymetry data collected from surveys during the past 20 years.

Previously, the pockmarks on the Chatham Rise were thought to have been produced by the release of methane through gas hydrate dissociation. However, recent geochemical investigations showed no indication of methane in the sediment cores. Current hypotheses for the formation of the pockmarks include groundwater fluid flow and the release of CO₂ modulated by CO₂ hydrates.

We present the results of the spatial analysis of the pockmarks on the Western Chatham Rise and whether there are any links between the location of pockmark formation and regional geology. The structures of the pockmarks were investigated to determine how the features were formed. The spatial configuration of the pockmarks were analysed vertically for stacking and laterally for potential ties to specific horizons, particularly horizons associated with Milankovitch order climate cycles. Results show stacking and clustering of pockmarks around specific horizons and a depth window in the upper sediment in which pockmarks are formed.

2D seismic data was interpreted to build a regional geology model, through relative stratigraphy from intersecting seismic lines through the survey area. This improves the current understanding of the stratigraphy along the Chatham Rise and Canterbury Shelf areas and places the pockmark field in a regional geologic context.