Characterisation and correlation of active hydrocarbon seepage using geophysical data sets: An example from the tropical, carbonate Yampi Shelf, Northwest Australia

For the first time in Australia, active present-day hydrocarbon seepage has been imaged—on the tropical carbonate Yampi Shelf, in 50 and 90m water depth. Seepage is evidenced by gas plumes in the water column that are associated with seabed features, such as clusters of reflective blocks, hard-grounds, pockmark fields, and mounds. Seepage activity and intensity seems to vary with changes in pressure related to macro-tidal cycles. The seabed features coincide with sub-surface features such as areas of seismic signal attenuation under high amplitude reflectors, seismic discontinuities and bright spots. Hydrocarbon migration-seepage pathways appear to be controlled by the reactivation of pre-existing fractures and dykes within the basement. The types of seabed features and their preservation on a tropical carbonate shelf are strongly influenced by the coarse bioclastic nature of sediments and the high energy of macro-tidal currents and storm reworking.