--> Biogenic Mounds in the Central Ceduna Sub-Basin: Implications for Hydrocarbon Migration

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Biogenic Mounds in the Central Ceduna Sub-Basin: Implications for Hydrocarbon Migration

Abstract

The Early Cenozoic in the Ceduna Sub-basin represents a transitional period from the rifting which separated Australia and Antarctica to the fast spreading of the Southern Ocean and development of a passive margin. This period is characterised by widespread igneous activity and the occurrence of biogenic mound complexes. In the proximal part of the Ceduna Delta (Eyre and northern Ceduna sub-basins) these mound complexes thrive on local topographic highs, exploiting the shut-down in silisiclastic sediment supply during the Eocene. New interpretation of 2D and 3D seismic data from the central Ceduna Sub-basin show additional Paleocene-Eocene biogenic mound complexes. They display rugose morphology, progadational and aggradational internal organisation and high impedance contrast with the surrounding sediments. These mounds typically show a clear relationship with underlying reactivated fault segments. These faults intersect potential oil mature Cretaceous source rock intervals and therefore one plausible mechanism for the development of palaeobathymetry unrelated mound complexes in the central Ceduna Sub-basin relies on fault related natural hydrocarbon seeps supplying nutrients for localised biogenic mound growth. The presence of a sub-bottom profile anomaly overlaid by a vertical water column acoustic contact, with morphology similar to hydro-acoustic flares observed in other hydrocarbon seep studies, in close vicinity of a mound complex support this model. The occurrence of seep related biogenic mounds would validate the presence of mature source rock(s) and hydrocarbon charge in the central Ceduna Sub-basin. If confirmed the biogenic mounds would imply fluid migration occurrence until at least the Eocene.