Triassic sediments of the Kaka Point Structural Belt, South Island, New Zealand, and their relationship to the Murihiku Terrane

The stratigraphy, palynofacies, palaeotemperatures (spore coloration, vitrinite reflectance), illite crystallinity, and carbonate stable isotope patterns (δ18O, δ13C) of the Triassic sediments exposed on the south-east Otago coast between Pilot Point and Roaring Bay are discussed in relation to the Hillfoot Fault and the differentiation of the Dun Mountain-Maitai and Murihiku terranes. Detailed sections, spore-pollen biostratigraphy, and palaeotemperatures are described from the Etalian Tilson Siltstone and Bates Siltstone at Kaka Point and from an undescribed Upper Etalian-Lower Kaihikuan succession at Campbell Point. New stable isotope analysis of diagenetic carbonates from the Triassic sediments of Campbell Point and Roaring Bay are included. Differences in the Triassic sediments to the north and south of the Hillfoot Fault are related to minor variations in their tectonic history and not to fundamental differences in depositional setting, lithofacies, and metamorphism. Higher palaeotemperatures and greater mineral alteration to the south of the Hillfoot Fault are interpreted as the effects of localised fluid flow along this structure when it acted as a zone of decollement in a fore-arc basinal setting under low or very low geothermal gradients. (author). 39 refs., 16 figs., 4 tabs