Potential oil formations in New Zealand, and their stratigraphic position as related to basin evolution

Abstract

Seven oil-prospective basins are recognised in New Zealand, and their stratigraphy is reviewed. Potential oil formations, which range in age from Upper Cretaceous to Pliocene, are discussed for each basin. Their particular position in the stratigraphic column is largely controlled by the local tectonic history. In anyone basin, possible source and reservoir rocks are in about the same stratigraphic position and generally closely related to each other. In five of the seven basins, which are characterised as epicontinental, unstable shelf areas, they generally occur near the base of the whole sedimentary sequence; this is shown to be inherent to the paleogeographic setting and particular tectonic evolution, and is consistent with the pattern found under similar conditions in other parts of the world. The characteristic lithologic assemblage of possible source sequences found here is of the shale-sandstone-coal type, and its environment is a transitional one of the near-shore marine and deltaic or estuarine-brackish to freshwater zone. Additional potential reservoir formations occur in some of the basins higher up in the section. They are formed by sandstone as well as carbonate rocks, and their presence is discussed in relation to the local tectonic history.