Carbonate rocks of offshore northern Zealandia

Thirty-eight non-tropical carbonate rock samples with subtropical affinities, from northern Zealandia, were obtained from oceanographic dredging expeditions in the Reinga-Aotea Basin (2013), and the Norfolk, Loyalty, and Three Kings ridges (2015). Samples range in age from Pleistocene to Paleocene and were petrographically classified into five depositional and one authigenic petrofacies: (1) coarse, bioclastic grainstone to packstone, (2) coarse, bioclastic packstone, (3) coated grains, (4) fine, bioclastic packstone, (5) wackestone, and, and (6) dolomite. The coarse grainstone, packstone and coated-grains petrofacies are dominated by >mm-scale bioclastic components indicating deposition in high energy continental shelf environments. These petrofacies show similarities to non-tropical carbonates such as the onshore New Zealand Oligocene Te Kuiti Group limestones. Fine bioclastic packstone and wackestone petrofacies, consistent with bathyal deposition, comprise primarily foraminfera and micrite, similar to Eocene fine-grained carbonates outcropping in New Zealand. The dolomite petrofacies comprises diagenetic dolomite similar to Paleocene and Eocene rocks of the Mead Hill and Amuri Limestone formations. Other post-depositional features are also directly comparable to onshore New Zealand limestones. Despite no clear relationship between age, lithology, or geographic location, this study shows that non-tropical shelf carbonates with subtropical affinities extend north beyond New Zealand (southern Zealandia) to at least 23.7°S latitude.