Abstract:
The upper Triassic and Jurassic (Marakopan to Heterian) rocks of the Marokopa area, which form part of the western limb of the Kawhia Syncline, are mapped lithologically in terms of units based on type sections at Kiritehere and Kawhia. The Kiritehere (200 m thick) and Ngutunui (1550 m) formations of the Arawi Group; the Arawhero Group, which could not be subdivided (1160 m); the Ururoa Shellbed (2 m) and Ururoa Formation (280 m) of the Ururoa Group; the Rengarenga Group, which could not be subdivided (570 to 930 m); the Oraka Sandstone (180 m), Captain King's Shellbed (1 m), Ohineruru Formation (280 to 700 m); the Kiwi Sandstone and Waikutakuta Formation of the Kirikiri Group. The last two formations interfinger and have a combined thickness of at least 240 m.
Sandy siltstones and fine sandstones are the dominant lithologies except in the Rengarenga Group, which consists largely of medium to coarse sandstones. Conglomerates are rare throughout. The petrology of the different rock types is discussed and an andesitic volcanic-granitic plutonic source suggested.
Eight species of rhynchonellid and three terebratuloid brachiopods, a scaphopod, nine gastropods, fourteen bivalves and a scalpellid barnacle are described. A number of these belong to genera not previously recorded from New Zealand.
Marwick's New Zealand Triassic and Jurassic stages are discussed and a modified zonal subdivision of the Otapirian, Ururoan and Heterian proposed.