The Petrel Sub-basin is an asymmetric, northwest-southeast trending Palaeozoic rift in the southeast portion of the Bonaparte Basin and contains mostly Palaeozoic and Mesozoic sediments.
The stratigraphy and structure of the sub-basin is illustrated by the two following regional seismic lines. Stratigraphic units dip regionally to the northwest about a northwest-plunging synclinal axis, resulting in exposure of lower Palaeozoic strata in the southern onshore area and in progressive subcropping of upper Palaeozoic to Tertiary strata offshore beneath Quaternary sediments.
These Phanerozoic formations exceed 15 km in thickness in the northern central Petrel Sub-basin.
The Vulcan Sub-basin is a northeast-southwest trending Mesozoic extensional depocentre in the western Bonaparte Basin and comprises a complex series of horsts, grabens and terraces. The Vulcan Sub-basin developed as an intra-continental graben in the late Callovian and structuring continued through to the Tithonian.
The stratigraphy and structure of the Vulcan Sub-basin are illustrated by the two following regional cross-sections.