Geophysical evidence for structurally-controlled, authigenic carbonate cementation in the Laminaria High, Bonaparte basin, Northwest Shelf of Australia

Abstract

3D seismic reflection data are used to investigate the processes which have led to the development of amplitude anomalies on reflectors in the faulted, Cenozoic overburden on the Laminaria High, Northwest Shelf of Australia. Amplitude and root mean square (RMS) attributes are mapped on two reflectors (seabed and horizon H9) that were deposited synchronous with fault activity and are located adjacent to predominantly ENE-WSW striking fault traces. On the seabed, the main anomaly is located on the up-dip side of the fault trace, and is elongated parallel to the local time structure contours. These observations are consistent with the anomalies having developed in response to structurally-controlled fluid seepage along, and up-dip migration away from the fault trace. The other amplitude anomalies associated with the H9 reflector are also located adjacent to fault traces but are discordant to the local time structure contours. The latter observation is inconsistent with the migration of buoyant fluid at the present day; instead, it suggests that the anomalies may be due to cemented hardgrounds that formed due to seepage when the faults intersected the palaeo-seafloor but were subsequently buried and deformed during ongoing sedimentation and fault growth/linkage. Prominent anomalies mapped on reflectors within the pre-faulting succession (H10) are located adjacent to, and are elongated along, sub-seismic scale, NW-SE striking faults or, as in the case of a deeper horizon (H13) show no clear relationship with the faults. We conclude that there is no relationship between the occurrence of anomalies and the magnitude of throw, or the duration of activity, along the Cenozoic faults. The results suggest that whilst fluid seepage and cementation were structurally-controlled, these processes were also influenced by permeability variations that cannot be resolved by seismic interpretation methods.