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Abstract
Warm‐water molluscs were transported to Wanganui Basin from the northeastern North Island during Pleistocene time as planktotrophic larvae. This is not possible at present, so their occurrence in Wanganui Basin correlates with breaches of the Auckland isthmus during high sea levels. The end of Nukumaruan time is clearly defined by the extinction of 29 genera of molluscs (most only locally) during this stage, including 15 at the end. The extinction likely was caused by the initial closure of the Auckland isthmus. Migrants to Wanganui from the northeastern North Island indicate that breaches of the isthmus during interglacials commenced in oxygen isotope stage (OIS) 25, just before the mid‐Pleistocene transition (MPT). Appearances of taxa from Australia at Wanganui during OIS 17–9 therefore indicate that warm‐water taxa were transported to New Zealand during interglacial maxima after the MPT. The migrants provide the first molluscan biostratigraphy at the OIS scale.
The Castlecliffian/Nukumaruan boundary, at the base of Ototoka tephra at Ototoka Beach, Wanganui, falls within OIS 57, with an age of c. 1.63 Ma. It is also dated at 1.63 Ma by the position with respect to the geomagnetic polarity time‐scale of three chemically indistinguishable tephra in ODP core 1123.
Neopanis new genus is proposed for "Isognomon” zealandicum (Suter, 1917) and related species. Notobotula molina (Fleming, 1959) (OIS 13) is a synonym of the North Atlantic‐Mediterranean genus and species Modiolula phaseolina (Philippi, 1844). Notospisula Iredale, 1930 and Spisula (Spisulona) Marwick, 1948 are regarded as synonyms of Spisula, sensu stricto, whereas "Spisula” aequilatera (Reeve, 1854) is referred to genus Crassula Marwick, 1948. Mactra (Mactrona) Marwick, 1952 is regarded as a synonym of Pseudocardium Gabb, 1869; Salacia Jukes‐Browne, 1914, Callanaitis Iredale, 1917, Eusalacia Cossmann, 1920, and Bassinaria Marwick, 1928 as synonyms of Circomphalus Mörch, 1853; Tawera Marwick, 1927 and Plurigens Finlay, 1930 as synonyms of Chamelea Mörch, 1853; and Lepsiella Iredale, 1912 and Lepsithais Finlay, 1928 as synonyms of Haustrum Perry, 1811. Brucetriphora, new name, replaces the homonym Tetraphora Laseron, 1958. New Zealand species previously referred to Pyrazus are transferred to Terebralia Swainson, 1840. Neopanis, Spisula, and Pseudocardium became extinct in New Zealand late in Nukumaruan time.
Arca cottoni Waghorn, 1926 and A. chambersi Beu, 1973 closely resemble living Pacific species, and likely were Pliocene migrants to New Zealand. Amygdalum striatum (Hutton, 1873) (late Miocene to OIS 9) is an earlier name for the Australian species A. beddomei Iredale, 1924. Limaria orientalis (A. Adams & Reeve, 1850) is common in Nukumaruan rocks, but is not recorded from Castlecliffian rocks before OIS 17. Laternula synthetica Marwick, 1948 (Pliocene, Auckland) is probably a synonym of the southeast Australian species L. laterna (Lamarck, 1818). Australian and western Pacific species that extended their ranges to New Zealand during late middle Pleistocene interglacial periods include: Anadara trapezia (Deshayes, 1839) (OIS 1 1–5e), a gryphaeid oyster, ?Parahyotissa imbricata (Lamarck, 1918)(OIS7), Bankivia fasciata (Menke, 1830) (OIS 11), Bembicium auratum (Quoy & Gaimard, 1834) (OIS 25,21, and 11), Diala semistriata (Philippi, 1849) (= Rissoa basispiralis Grant‐Mackie & Chapman‐Smith, 1971) (OIS 7), Pyrazus ebeninus (Bruguière, 1792) (= Zeacumantus delicatus Laws, 1950) (Pliocene and OIS 7), Capulus danieli (Crosse, 1858) (= Pilaeopsis uncinatus Hutton, 1873) (OIS 9, 7), Eunaticina papilla (Gmelin, 1791) (= Sigaretus cinctus Hutton, 1873) (OIS 9, 7), Brucetriphora granifera (Brazier, 1894) (= Notosinister tepikiensis Powell, 1934) (OIS 7), Coralliophila mira (Cotton & Godfrey, 1932) (= Murexsul tepikiensis Powell, 1934) (OIS 7), Pupa affinis (A. Adams, 1855) (= Buccinulus kirki Hutton, 1873, = B. albus Hutton, 1873, = B. gracilis Kirk, 1882) (OIS 9‐Recent), Leucotina casta (A. Adams, 1853) (= Odostomia sulcata Hutton, 1885, = Admete(?) ambigua Hutton, 1885) (late Nukumaruan‐Recent), and Akera soluta (Gmelin, 1791) (OIS 7). The Pacific oyster, Crassoastrea gigas (Thunberg, 1793), is recorded from Ohope, Whakatane (OIS 15?) and from a sample dredged in the Bay of Plenty, radiocarbon dated at 37 000–40 000 yr BP (OIS 3), demonstrating that this species extended its range to New Zealand naturally in the past.
Notes
Institute of Geological & Nuclear Sciences, P.O. Box 30 368, Lower Hutt, New Zealand. Email: [email protected]
