Stratigraphic development and petroleum prospectivity of northern Zealandia

Northern Zealandia lies between Australia, New Zealandia, and New Caledonia. It has an area of 3,000,000 km2 and is made up of bathymetric rises and troughs with typical water depths of 1000 to 4000 m. I use 39,309 line km of seismic-reflection profiles tied to recent International Ocean Discovery Program (IODP) drilling and three boreholes near the coast of New Zealand to investigate stratigraphic architecture and assess the petroleum prospectivity of northern Zealandia.  Sparse sampling requires that stratigraphic and petroleum prospectivity inferences are drawn from better-known basins in New Zealand, Australia, New Caledonia, TimorLeste and Papua New Guinea. Five existing seismic-stratigraphic units are reviewed. Zealandia Seismic Unit U3 is sampled near New Zealand and may contain Jurassic Muhiriku Group coals. Elsewhere, Seismic Unit 3 may have oil-prone equivalents of the Jurassic Walloon Coal Measure in eastern Australia; or may contain Triassic-Jurassic marine source rocks, as found in offshore Bonaparte Basin, onshore Timor-Leste, and the Papuan Basin in Papua New Guinea. Seismic Unit U2b (Mid-Cretaceous) is syn-rift and may contain coal measures, as found in Taranaki-Aotea Basin and New Caledonia. Seismic Unit U2a (Late Cretaceous to Eocene) contains coaly source rocks in the southeastern part of the study area, and may also contain marine equivalent carbonaceous mudstone, as found at Site IODP U1509. Unit U2a is transgressive, with coaly source rocks and reservoir sandstones near its base, and clay, marl and chalk above that provides a regional seal. Seismic Unit U1b (Eocene-Oligocene) is mass-transport complexes and basin floor fans related to a brief phase of convergent deformation that created folds in the southern part of the study area and regionally uplifted ridges to create new sediment source areas. Basin floor fans may contain reservoir rock and Eocene folding created structural traps. Seismic Unit U1a is Oligocene and Neogene chalk, calcareous ooze, and marl that represents overburden. Mass accumulation rates (MAR) and climatic temperatures were high in the late Miocene and early Pliocene, resulting in peak thermal maturity and hydrocarbon expulsion at ~ 3 Ma.  Approximately one-fifth of the region has adequate source rock maturity for petroleum expulsion at the base of Seismic Unit U2: Fairway Basin (FWAY), southern New Caledonia Trough (NCTS) and Reinga Basin (REIN). Plays may exist in either Seismic Unit U3 or U2, with many plausible reservoir-seal combinations, and several possible trapping mechanisms: unconformities, normal faults, folds, or stratigraphic pinch-out. The rest of the region could be prospective, but requires a source rock to exist within Seismic Unit U3, which is mostly unsampled and remains poorly understood.