Characterization and restoration of inverted features across the southern Taranaki Basin

Abstract

The Southern Taranaki Basin is a predominantly offshore basin located between the two islands of New Zealand. The basin has a complex structural history due to its current location along an unconventionally shaped plate boundary and changes in a tectonic regime that have affected the basin over the last ~80 m.y. The focus of this study is the restoration and strain analysis of the Southern Taranaki Basin, which consists of the Central Graben and the Southern Inversion Zone. 2D and 3D seismic data sets are interpreted across the Southern Taranaki Basin using Schlumberger’s Petrel to create seven horizons that represent boundaries between significant structural events. The horizons and transecting fault surfaces are transferred to cross sections perpendicular to the major structures, which are each restored sequentially in 2D using Midland Valley’s Move. The restorations incorporate unfaulting, unfolding, and decompaction to measure the strain within each section and assess the overall distribution of strain within the Southern Taranaki Basin. Cretaceous extension associated with rifting and break-up of Eastern Gondwana shows a range of 8.1% - 0.8% extension along the cross sections. Localized basin extension in the Eocene (tied to the initiation of spreading between the Pacific and Australian plates in the southwest) resulted in a 1.9 - 0% extension. During the Oligocene-Miocene, Pacific Plate subduction beneath the North Island began to the northeast, resulting in 6.1 - 0.1% shortening. Within the last 7 m.y., as shortening continued in the south of the Southern Taranaki Basin, back-arc extension migrated from the north, resulting in up to 1.8% extension in the northern sections, up to 0.5% shortening across the southern end of the study area, and no strain in sections in the middle of the study area. Across the Southern Taranaki Basin, the net change along the lengths of individual sections range between 7.8% shortening and 2.7% extension. This study shows that the latitudinal transition of strain over time across Southern Taranaki Basin is not as uniform as previously assumed.