The Ordovician-Permian Southern Carnarvon Basin is a large, mainly onshore basin on the Western Australian poly-phased margin. About 30 exploration wells have been drilled including just two offshore wells. Minor gas shows have been encountered in some wells but there are no discoveries to date. Exploration has yet to confirm the potential of the area.
The basin consists of the Gascoyne, Merlinleigh, Bidgemia and Byro Sub-basins and Bernier Platform and is flanked to the east by the Archaean Pilbara Block. The Gascoyne Sub-basin comprises a broad, low-amplitude syncline with two distinct depocentres that contain up to 5 km of Ordovician-Devonian strata and a thin Cretaceous-Cainozoic cover. The other three sub-basins contain up to 7 km of predominantly Permo-Carboniferous sediments with a Mesozoic veneer, which thickens to the north and west. Faults trend northerly and northwesterly.
The structural evolution of the Southern Carnarvon Basin occurred mainly from the Ordovician-Silurian to the Late Permian. The basin was initiated as an epicratonic rift in the Late Ordovician-Early Silurian and rifting was accompanied by uplift of the Pilbara Block. Shallow marine to tidal flat conditions were established in the Late Silurian. Following a period of non-deposition during the Early Devonian, Devonian and Early Carboniferous sediments were deposited across a shallow marine shelf and an interior-sag basin. Marine conditions were terminated in the mid-Carboniferous by a major tectonic episode, the collision between Gondwanaland and Laurasia to form the super-continent Pangea. Most of the basin and the adjacent Pilbara Block were uplifted at this time. Renewed rifting in the Late Carboniferous to Early Permian activated the Wandagee, Kennedy Range and Darling Fault systems and initiated a second phase of deposition in the Merlinleigh, Byro and Bidgemia Sub-basins. Glacial conditions dominated the Late Carboniferous and Early Permian.
Source rock data is sparse, but indicates excellent gas-prone source rocks in the Early Permian and excellent/good oil-prone source rocks in the Early Ordovician, Late Devonian, Early Carboniferous and Late Permian. Reservoir targets are the Ordovician Tumblagooda Sandstone, the Devonian Kopke Sandstone, Nannyarra Sandstone and Point Maud Member reefs and the Permian Moogooloo Sandstone, Byro Group equivalent sandstones and Chinty Formation.
Further information on the Southern Carnarvon Basin can be found in the Western Australia Atlas of Petroleum Fields in the onshore Carnarvon Basin (Ellis and Jonasson, 2001).