Taitai Series (Early Cretaceous) and the elimination of the Mokoiwian Stage

Abstract

The Mokoiwian Stage (supposedly Neocomian-Aptian) in its type area, Tapuaeroa Valley, Raukumara Peninsula, contains Motuan (Albian) macrofossils, Albian-Cenomanian dinoflagellates, and Foraminifera of undifferentiated Motuan-Ngaterian age. The Mokoiwian Stage is therefore equivalent to at least part of the Motuan and is suppressed in favour of the latter. Motuan sequences in Raukumara Peninsula, Wairarapa, and Marlborough contain specimens of Inoceramus which are probably conspecific with I. warakius, the sole index species of the Mokoiwian Stage as originally defined. Rocks in several districts mapped as Mokoiwian on stratigraphic position, lithology, or the presence of poorly preserved shell fragments of Inoceramus, and occurring below fossiliferous Motuan or Ngaterian, are probably of early Clarence (Urutawan to Motuan, Albian) age. The remaining stage in the Taitai Series, the Korangan (late Aptian), unconformably overlies Torlesse-like rocks (Late Jurassic-Early Cretaceous) in its type area and is overlain unconformably by the Urutawan (Middle-Late Albian), the oldest stage of the Clarence Series. No pre-Korangan Early Cretaceous fossils are known in New Zealand, the lower and upper limits of the Taitai Series and the upper limit of the underlying Oteke Series (Late Jurassic) are poorly defined, and there is at present no convincing evidence of continuity of deposition from Late Jurassic into and through the Early Cretaceous. Consequently, until definitive studies of Early Cretaceous rocks and their relation to Jurassic rocks are completed, it is recommended that Taitai Series be defined as the rocks deposited in the interval of time between the upper limit of Oteke Series and the lower limit of Clarence Series, i.e., grossly earliest Neocomian to latest Aptian, although a latest Tithonian to earliest Albian time span cannot be discounted.