Haines Structure: a probable Eocene complex impact structure in the offshore Canning Basin,Western Australia

A seismic structure imaged in a single 2D seismic profile from the offshore Canning Basin, Western Australia, is interpreted to be a possible complex impact crater on the basis of its seismic character. The feature, herein referred to as the Haines Structure, is symmetrical in two dimensions over ～2.5 km and comprises a centrally uplifted basal surface, a depressed upper surface, a highly deformed intervening package and an overlying horizon that is ‘sagging’ over the depression. The possible impact structure lies within carbonate units of Eocene or Early Oligocene age as determined from seismic correlation to petroleum exploration wells. The structure has not been drilled; therefore distinguishing characteristics used to define an impact origin, such as shock metamorphism, are not available. Comparison with other features in the Neogene succession of Australia's North West Shelf that have previously been interpreted as impact structures highlights the presence of key elements in the Haines Structure that characterise known complex impact craters, and the absence of seismic features related to alternative processes, such as a link to deeper structures that would be expected beneath a volcanic pipe.