| Summary: | The Late Cretaceous-Cenozoic geology of New Zealand represents the evolution of a post-Gondwana, Pacific-facing passive margin which interacted, first, with the mid-Cenozoic development of the Australian/Antarctic and Australian/Pacific plate boundaries and, second, with the subsequent development of the oceanic thermohaline circulation system. Situated between the Tasmanian and southwest Pacific oceanic current gateways, the stratigraphy of the New Zealand region provides our best record of the evolution of the Pacific Ocean's largest deep cold-water inflow, the Deep Western Boundary Current (DWBC), and also possesses an important record of Antarctic Intermediate Water flow. Prior to Leg 181, our knowledge of southwest Pacific Ocean history and, in particular, the development of the DWBC and its local partner, the Antarctic Circumpolar Current (ACC), was poor. Seven holes were therefore drilled east of New Zealand to determine the stratigraphy, sedimentary systems, and paleoceanography of the DWBC, ACC, and related water masses and fronts. The sites comprised a transect of water depths from 396 to 4488 m and spanned a latitudinal range from 39° to 51°S. Leg 181 drilling provided the data needed to study a wide range of problems in the Southern Ocean Neogene. Driven by rifting and a new cycle of seafloor spreading along the Mid-Pacific Rise, New Zealand's youngest (Kaikoura) stratigraphic cycle begins with Late Cretaceous rift fill followed by subsidence and marine transgression until the late Eocene. Biopelagic oozes accumulated throughout as an abyssal apron around the Pacific perimeter of the New Zealand Plateau, seen as Paleocene siliceous nannofossil chalk, chert, and clay at Site 1121 (water depth = 4488 m) and nannofossil chalk at Site 1124 (water depth = 3967 m). At the Eocene/Oligocene boundary (~33.7 Ma), the spreading ridge between Australia and Antarctica broke through south of the Tasman Rise, linking for the first time the Indian and Pacific Oceans into a continuous Southern Ocean. Powerful ...
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