Inoceramid bivalves from the Late Cretaceous of New Zealand

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Crampton, J.S. 1996 Inoceramid bivalves from the Late Cretaceous of New Zealand. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences monograph 14; New Zealand Geological Survey paleontological bulletin 70 188 p.

Abstract: In New Zealand Inoceramids are by far the most numerous macrofossil group in Cretaceous strata, being widespread on the East Coast from Marlborough to Raukumara Peninsula, and in Northland. This study revises the upper Cenomanian to Santonian (Upper Cretaceous) taxa from New Zealand, and describes their biostratigraphy, correlations and mode of life. A total of eight species and six subspecies are described: Inoceramus australis Woods, 1917 (middle - upper Piripauan Stage); I. opetius Wellman, 1959 (Teratan Stage); I. pacificus pacificus Woods, 1917 (lower Piripauan Stage); I. pacificus nanakius subsp. nov. (lower Piripauan Stage); I. spedeni sp. nov. (upper Mangaotanean - lower Teratan stages?); I? madagascariensis (Heinz, 1933)(=I. nukeus Wellman, 1959, Teratan Stage); Cremnoceramus bicorrugatus bicorrugatus (Marwick, 1926)(middle - upper Mangaotanean Stage); C. bicorrugatus matamuus subsp. nov. (lower Mangaotanean Stage); C. moorei sp. nov. (upper Mangaotanean Stage?); Magadiceramus? rangatira rangatira (Wellman, 1959)(middle - upper Arowhanan Stage); and M? rangatira haroldi subsp. nov. (lower Arowhanan Stage). Seven inoceramid biozones are defined. New biostratigraphic data are used to revise the definitions of New Zealand Upper Cretaceous chronostratigraphic units. Emended definitions of the Arowhanan, Mangaotanean and Teratan stages (Raukumara Series, upper Cenomanian - middle Coniacian) are based on an existing and adequate type section in Mangaotane Stream, Raukumara Peninsula. The Pirpauan and Haumurian stages (Mata Series, upper Coniacian - Maastrichtian) remain poorly defined from a problematic type section at Haumuri Bluff, Marlborough. The existing definition of the Haumurian Stage is based primarily on the lowest occurrence of an ''inoceramid'' of dubious taxonomic status. Revised correlations between the New Zealand and international timescales are (in ascending order): Arowhanan Stage~upper Cenomanian to upper Turonian, Mangaotanean Stage~upper Turonian to lower Coniacian, Teratan Stage~middle Coniacian, Piripauan Stage~upper Coniacian to middle Santonian. The taxonomic utility of two little-studied morphological characters, ligament area morphology and microstructure of the ligamentat are assessed in detail for two species. Whereas intraspecific and ontogenetic variability can be very substantial, there is little doubt that these characters have considerable potential to distinguish taxa at the specific and subspecific levels. Inoceramids occur within a wide range of facies and sedimentary rock types. They were widely distributed within the marine realm, from the inner shelf to depths of at least 4500 m. They are abundant in low diversity or monospecific faunal assemblages and/or in strata that were probably deposited under dysaerobic conditions. (auth/JED)

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