The Cenozoic geology of the Gisborne area (1:50 000 metric sheet Y18AB), North Island, New Zealand

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Abstract
Strata in the Gisborne area, North Island, New Zealand, are chiefly Neogene, whereas rafts of Cretaceous and Paleogene age crop out within diapirs which intrude the Neogene strata. The Cenozoic sequence commences with the Oligocene Weber Formation, Whangara Sandstone, and the Waiomoko Formation, which are followed by the early Miocene Whitiwhiti, Waremapou and Tuaheni Point Formations (which form the lower part of the Tolaga Group). The Tuaheni Point Formation was deposited from centripetal‐flowing turbidity currents within a small slope‐basin like those now present offshore. The upper part of the Tolaga Group, which is late Miocene to Pliocene in age, cannot be subdivided on lithology and it is mapped in stage units (Waiauan, Tongaporutuan, Kapitean, and Opoitian). However, locally distinctive rock types, defined within stages, are mapped as members. (Puketapu Tephra, Tarewarewa Sandstone, Pututahi Limestone, Papatu Sandstone and Waipura Sandstone). Like the early and mid‐Miocene strata, the Waiauan and Tongaporutuan Stages were deposited in a slope basin, whereas Kapitean and Opoitian strata show the construction of substantial soudieastward‐growing continental slopes, which are considered to indicate a forearc basin environment. Structure within the sheet district is chiefly represented by faults and diapirs. No late Quaternary faults are known, but diapir growth occurred during the Tongaporutuan, and a diapir east of Gisborne was active in 1931.