This Feature Dataset contains contours that depict the interpreted depth below sea level (in metres) to the N60 seismic horizon (c. 4 Ma; approximates base Pliocene; New Zealand Late Opoitian sub-Stage), as mapped within the Northwest Province of the Atlas of Petroleum Prospectivity (namely the Taranaki, Deepwater Taranaki, and Reinga-Northland basins). Contour intervals are 250 m. For more information about the seismic horizon naming scheme used in this project please refer to: Strogen, D.P.; King, P.R. 2014. A new Zealandia-wide seismic horizon naming scheme. Lower Hutt, NZ: GNS Science. GNS Science report 2014/34. 20 p. The depth grids, from which these contours were derived, were generated in Paradigm 2015 SeisEarth software using an adaptive fitting algorithm and a grid resolution of 1 km x 1 km. Faults have not been incorporated into the regional-scale gridding of either the TWT or depth maps in this project. The depth grids were then exported from SeisEarth (Zmap format), checked for internal consistency in Zetaware (Trinity 4.61), edited as needed to account for gridding errors and then exported as ArcView Ascii grids, imported and contoured with Esri's ArcGIS software. For more information about the depth conversion and gridding process used, please refer to: Arnot, M.J. and Bland, K.J. et al. (Compilers), 2016. Atlas of Petroleum Prospectivity, Northwest Province: ArcGIS geodatabase and technical report. GNS Science Data Series 23b. Given the considerable variability in the spacing and density of 2D seismic data over the entire NWP area the "smoothness" of the depth maps varies accordingly. In the central Taranaki Basin, where seismic line spacing may be 5 km or less, the 1 km x 1 km grid resolution captures the geological complexity well. However, in areas of the NWP such as the Deepwater Taranaki Basin to the west and Reinga Basin in the north, seismic line spacing may be in the order of 15 to 30 km. In such areas the underlying geological complexity is only captured where seismic interpretation exists along the available 2D seismic lines.