Provenance analysis of the Late Cretaceous to Paleocene Rakopi, North Cape, and Farewell formations, northwest Nelson, New Zealand

• Main Author: Smithies, Sarah Lynette
• Format: Other/Unknown Material
• Language: English
• Published: University of Canterbury 2018
• Subjects: New Zealand; North Cape; Separation Point
• Online Access: http://hdl.handle.net/10092/15581; https://doi.org/10.26021/8970

The Taranaki Basin of New Zealand first developed in the middle of the Cretaceous as Zealandia rifted from Gondwana. Rift basins were active depocentres throughout the Late Cretaceous to Paleocene when rifting slowed. The only outcrops are located in northwest Nelson in the Pakawau sub-basin, a northeast trending graben bound by the Wakamarama Fault to the southeast and the Kahurangi Fault to the northwest. This study focuses on the provenance of the Late Cretaceous Rakopi and North Cape formations of the Pakawau Group and the Paleocene Farewell Formation deposited within the Pakawau Sub-basin. There are a range of potential basement sources, including the metasedimentary units of the Buller and Takaka terranes, granitoids of the Separation Point Suite and Karamea Suite, volcanics of the Takaka Terrane, and a variety of schists. The depositional environments of the Rakopi, North Cape, and Farewell formations provides the context for the provenance analysis undertaken in this thesis. Previous studies were reviewed, and additional data added from outcrop description, paleoflow measurements, and measured stratigraphic columns. The oldest unit is the Late Cretaceous Rakopi Formation which contains sandstones, carbonaceous mudstones, siltstones, minor conglomerates, and coal, interpreted as a meandering river and floodplain environment. Locally at the base of the Rakopi Formation is the Otimataura Conglomerate; conglomerates, breccias, and sandstones interpreted as alluvial fans fed from the Wakamarama fault scarps. The Late Cretaceous North Cape Formation conformably overlies the Rakopi Formation and contains sandstones, siltstones, carbonaceous mudstones, thin coal seams, and rare conglomerates. It is interpreted as a marginal marine deposit with sediment contributions from fan deltas prograding from the Wakamarama Fault into a shallow marine embayment. New work on the Paleocene Farewell Formation has led to three lithofacies associations being proposed. Association FM has trough cross-bedded sandstone beds in ...