The Reinga Basin, North Island, New Zealand

Abstract

In early 2009, CGGVeritas, supported by the Crown Minerals Group of New Zealand’s Ministry of Economic Development, undertook a 5,900 km reconnaissance 2D seismic survey of the Reinga Basin, which is located to the northwest of the Northland Peninsula and Basin, New Zealand. Although very little data previously existed across this basin apart from low-fold reconnaissance seismic data, it was suspected of being an extension of the Northland Basin and to contain a thick sedimentary succession. It was thought to have formed as a rift basin near the Gondwana margin and to have been inverted during Neogene evolution of the present plate boundary. This paper is the result of the first interpretation of this new, high-quality data set. It confirms the presence of the basin and its sedimentary succession. Up to 9,000 m of sedimentary fill is imaged. The presence of coaly early rift packages and extensions of the Waipawa Formation black marine shale suggest that the basin contains voluminous source rocks. The basin appears to be more deformed in the northwest where large inversion structures are imaged. The northeastern margin is underlain by an extension of the Northland Allochthon which was obducted onto the New Zealand margin during initiation of the present plate boundary around 25 million years ago (Ma). The basin may also have been affected by strike-slip faulting associated with the Vening-Meinesz fracture zone, which developed during the Miocene. Several volcanic bodies are recognised, but in contrast to the adjacent Northland Basin where many large Miocene shield volcanos erupted, volcanic extrusions are rare in the Reinga region. Thermal modelling suggests that the basal source rocks are mature and expelling hydrocarbons and many direct hydrocarbon anomalies are present. Large trapping structures are apparent throughout the basin and even at this early stage of knowledge it appears that the region may have significant hydrocarbon potential. This paper will discuss the evolution of the basin in the regional tectonic context and summarise its petroleum prospectivity.