Pockmark-like structures on the Poverty Bay sea bed — possible evidence for submarine mud volcanism

Abstract

Abstract Side-scan sonographs of the shallow (2–22 m) sea floor off Gisborne Harbour, northern Poverty Bay, New Zealand, include areas of scattered to locally prominent, subcircular, flat-floored depressions, resembling pockmarks, typically 5–20 m across and 0.3–0.5 m deep, in muddy very fine sands. Because of their geologic setting, it is speculated that the structures are exhalative pits for ascending streamers of mud, water, and/or natural gas from underlying diapiric intrusions of predominantly Paleogene shale, and that they may be submarine equivalents of the subaerial quiescent mud volcanoes occurring in the Gisborne district. Because of their possible significance in hydrocarbon prospecting, tsunami generation, and siting of subsea cables, pipelines, and offshore structures, they require further research.