THE RELATIONSHIP BETWEEN LINEAR CHAINS OF POCKMARKS AND SHALLOW SEISMIC STRUCTURE, PASSAMAQUODDY BAY, NEW BRUNSWICK, CANADA

The floor of Passamaquoddy Bay, New Brunswick is a largely muddy seabed which is densely populated with pockmarks of uncertain origin. The regional distribution has been described initially by Fader et al. (1988) based on reconnaissance sidescan sonar and seismic reflection profiles. Subsequent multibeam coverage of nearly the entire bay floor has confirmed the pockmark distribution and provided much more detail on their specific geometry. The highest densities occur between Navy and Deer Islands where the pockmarks frequently occur as linear chains. The trend of almost all the linear chains is predominantly NW-SE which is parallel with the alignment of large scale glacial fluting apparent in the provincial topographic relief.

A grid of sub-bottom profiler transects was constructed to investigate the relationship between the surface expression of the pockmarks and the underlying shallow sedimentary structure. Interpretation of these profiles show that the pockmarks are all developed in an upper acoustically-transparent unit, with deepest pockmark penetration extending just to the base of this unit. No fault offsets, associated with the linear chains of pockmarks, were observed at the base of the unit. This surface unit overlies an erosional unconformity. Below the unconformity, two units of contrasting acoustic facies define a strong structural relief in the order of 10-30m (although some of the highs appear to be truncated at the unconformity). The predominant structural orientation of the highs is NW-SE. The chains of pockmarks preferentially appear along the boundaries of these structural highs.