Integrated outcrop, drill core, borehole and seismic stratigraphic architecture of a cyclothemic, shallow‐marine depositional system, Wanganui Basin, New Zealand

Abstract

Late Pliocene to mid‐Pleistocene (c. 2.1–0.4 Ma) strata exposed in the, now classical, Nukumaru and Castlecliff coastal cliff sections north‐west of Wanganui comprise 25, 6th (41 ka) order and 5th (100 ka) order, shallow‐marine to marginal marine stratigraphic sequences, deposited during global glacioeustatic sea‐level cycles corresponding to Marine Isotope Stages (MIS) 78–10. Here, we characterise the sequences using: (1) a series of drill cores sited above and behind the coastal outcrops, which recovered a composite record of c. 450 m, (2) a new high resolution multichannel seismic reflection profile acquired along the beach adjacent to the coastal cliffs, and (3) downhole digital logs from the boreholes. This paper integrates the outcrop and subsurface datasets to produce a high resolution model of the stratigraphic signatures and 2D architecture of a cyclical, shallow‐marine deposition system. Such models have significant applications to petroleum exploration, and enable the distribution of reservoir facies and intervening seal rocks within sequences, together with the nature of the connectivity of sandstone facies between sequences, to be evaluated. Similar hydrocarbon‐producing systems within the Eocene Kapuni Group (e.g., Mangahewa and Kaimiro formations) have been, and are still, the focus of intense exploration in Taranaki Basin.