Two-dimensional seismic reflection data from offshore southern Australia image a series of 2–13 km wide by 50–800 m high, sub-circular, Middle Eocene age mounds. The majority of the mounds occur above tips of igneous bodies intruded into the underlying Upper Cretaceous succession. The mounds are interpreted as the seismic expression of submarine volcanic vents, which are amongst the largest and oldest examples ever documented. These vents are pristine and have been preserved because of their submarine environment of emplacement and burial in a post-eruption, sediment drape.

Supplementary material:

Uninterpreted version of the seismic sections presented in Figure 3 is available at www.geolsoc.org.uk/SUP18545.

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