Guide to New Zealand Bolivinita (Foraminifera; Neogene - Quaternary) (MON 28-pdf)

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Scott, G.H. 2017 Guide to New Zealand Bolivinita (Foraminifera; Neogene - Quaternary). Lower Hutt: GNS Science. GNS Science monograph 28. 127 p.; doi: 10.21420/G2459G

Abstract: The biserial benthic foraminiferal genus Bolivinita is widely represented in New Zealand Late Miocene – Recent shelf and bathyal environments and several of its species are useful in regional biostratigraphy. To advance the stratigraphic application of the genus, the external morphology and population variation of several of the more widely distributed species are reviewed, and their biogeography and stratigraphy are summarized. Detailed accounts are given of Bolivinita compressa Finlay, B. finlayi Kennett, B. medialis Scott n. sp., B. pliobliqua Vella, B. pliozea Finlay, B. pohana Finlay, B. pseudocompressa Crundwell n. sp., B. quadrilatera (Schwager), B. quadrilatera granttaylori Vella and B. urenuia Scott n. sp. Bolivinita pseudocompressa Crundwell n. sp., B. obconica Crundwell n. sp. and B. striata Crundwell n. sp. are proposed in the appendices. Bolivinita elegantissima Boomgaart, B. subangularis (Brady) and an undescribed species are illustrated and noted; they are not examined in the main study. Taxa are described and illustrated in three standard orientations (spiral, axial, distal) and terminology is introduced for the major architectural elements, especially those seen in the shell outline. Important features are identified on plates that illustrate intra-sample variation. The spiral outline is regarded as particularly useful because of its clear presentation of chamber components and shell geometry. It is the best orientation for differentiating between taxa with bilaterally symmetrical shells (Bolivinita quadrilatera, B. medialis, B. pliozea ) and those with rhomboidal shells (B. compressa, B. finlayi, B. pohana, B. pliobliqua, B. pseudocompressa, B. urenuia ). Ordinations and cluster analyses of coefficients of elliptical Fourier curves fitted to outline coordinates of shells in spiral orientation are used to portray intra- and inter-sample variation, and to assist in the discrimination of taxa. Stratigraphically, attention is focused on the lowest and highest occurrences of taxa and their regional distributions. A principal biogeographic feature of the group is the appearance of Bolivinita compressa, B. medialis, B. pohana and B. quadrilatera in close proximity (probably as migrants) in the New Zealand record at the base of the Tongaporutuan Stage (base of Late Miocene, c. 11 Ma). These taxa represent most of the shell designs found in the group. In upward order Bolivinita urenuia, B. pliobliqua, B. pliozea, B. finlayi and B. pseudocompressa appeared in the Late Miocene - earliest Pliocene. Architecturally, most resemble earlier taxa and several may be their descendants. Intra- and inter-sample variation is often large and complicates the recognition and discrimination of taxa. Several species are interpreted as polytypic although some populations presently interpreted as intra-specific variants may warrant formal recognition. The record of speciation events is poor and the phyletic history of Bolivinita in New Zealand is obscure. Bolivinita was widely distributed in onshore Late Miocene bathyal environments in New Zealand. Generally, species of Bolivinita were minor components of Late Miocene benthic foraminiferal assemblages but were often persistent. Localized blooms of rhomboidal taxa (e.g., B. compressa, B. pohana ) suggest that they could be opportunists. In the Kapitean Stage (latest Miocene) the distribution of the principal rhomboidal species (B. compressa ) contracted, although the record may be biased by the prevalence of shelf sedimentation in New Zealand basins at this time. Concurrently, B. pliozea , a bilaterally symmetrical design, evolved from a weakly rhomboidal ancestor (B. pliobliqua ). It became widespread in Pliocene outer shelf and upper bathyal assemblages and persisted into the Pleistocene. There are few younger records and it is unlikely that it is a member of the Recent fauna. Bolivinita pseudocompressa, the principal Pliocene rhomboidal species, was largely restricted to one basin. Records of the globally-distributed Bolivinita quadrilatera (one of the original migrants), are sporadic through its long presence in the New Zealand region. (auth)