Structure and petroleum potential of the Taranaki fault play (original) (raw)

Abstract

The Taranaki Fault is a crustal scale thrust of at least 400 km in length that lies at the eastern margin of the Taranaki Basin. Interpretation of seismic-reflection data (including pre-stacked depth migrated lines), tied to recently drilled wells, indicates that the dip of the principal fault surface ranges from 25 to 45° and increases southwards. The principal fault is corrugated on length scales of 10’s to 100’s of kilometres and is accompanied by multiple slip surfaces which often splay from the main fault within 2-5 km of the upper tip. Splays can be entirely within Tertiary or basement rocks, or may produce inter-fingering of basement and CretaceousTertiary strata. These splays are discontinuous and, in the main, appear to extend for no more than 10-50 km along strike. The fault has accommodated at least 12-15 km of dip-slip displacement in the last ca. 80 Myr. Analysis of displacement data indicates at least two periods of accelerated shortening and displacement on the fault, during the Mid-Late Eocene (ca. 43-35 Ma) and the Early Miocene (ca. 23-18 Ma). These periods of more rapid deformation are interspersed with intervals during which contraction was either slow or absent. The relative importance of Eocene and Miocene displacements varies along the length of the fault with a greater proportion of Eocene and Miocene displacement north and south of Pukearuhe-1 well respectively. This distribution of displacement reflects a southward migration of fault activity which is mirrored by an apparent southward migration of basin depocenters adjacent to the fault. Deformation and associated movement of the Taranaki Fault has produced changes in fault dip, anastomosing fault splays and corrugations in the principal thrust surface together with tilting and folding of sedimentary strata adjacent to the fault. Therefore, petroleum accumulations underneath the fault are most likely to be spatially discontinuous, but potentially stacked within the fault zone.

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