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doi:10.2204/iodp.proc.317.209.2015

Results

At least 149 ostracode species belonging to 60 genera were identified from 142 samples from Holes U1354B and U1354C, although two samples collected from 147.1 and 147.6 mbsf contained no ostracodes (Table T1; Plates P1, P2, P3). The number of specimens per gram of dried sediment ranges between 0 and 143.7 (Fig. F2). High abundance values (>100 specimens) were identified from samples at 13.5, 66.4, 106.9, and 111.1 mbsf. Low abundance values (<1) were found in samples at 88.3, 101.9, 102.4, 133.0, 136.0, 146.1–152.1, 212.2, 279.3, 308.1, 317.4, and 375.0 mbsf. The species diversity in 113 samples containing more than 50 specimens ranges between 1.49 and 3.18. Relatively low values were found in samples at 52.9, 95.3, 106.9, 121.0, 121.5, 127.5, 130.5–136.0, 148.1, and 151.1 mbsf, and high values were found at 11.6, 13.5, 14.5, 18.6, 55.9, 58.3, and 88.3 mbsf. The equitability ranges between 0.6–0.9.

Temporal exchanges of dominant taxa were frequently found throughout the section (Fig. F3). There are 42 ostracode taxa that occupy >10% of the total abundance in each sample containing >50 specimens. Of these, the 18 taxa that occupied more than 20% are the following: Actinocythereis tetrica, Argilloecia spp., Bradleya opima, Callistocythere sp. 1, Cytherois parallella, Cytheropteron sarsi, Cytheropteron wellingtoniense, Cytheropteron willetti s.l., Hermanites briggsi, Hemicytherura gravis, Kotoracythere formosa, Loxoconcha australis, Munseyella brevis, Munseyella cf. punctata, Munseyella sp. 4, Oculocytheropteron acutangulum, Oculocytheropteron sp. 1, and Pellucistoma coombsi. Many of these inhabit the inner to outer shelf around New Zealand and Australia (e.g., Hornibrook, 1952; Swanson, 1979a, 1979b; Yassini and Jones, 1995; Swanson and Ayress, 1999; Webber et al., 2010), suggesting that dominant ostracode species on the Otago shelf have not changed since the late Pliocene. Cytheropteron sarsi, Cytheropteron willetti s.l., Hemicytherura gravis, Munseyella brevis, Oculocytheropteron acutangulum, and Argilloecia spp., which inhabit the middle to outer shelf, are abundant throughout the entire section (Fig. F3). Conversely, taxa living in the inner to middle shelf, such as Kotoracythere formosa, Cytheropteron wellingtoniense, and Hermanites briggsi, and in the outer shelf, such as Bradleya opima and Pellucistoma coombsi, displayed relatively high abundances in several horizons. These horizontal patterns might be considered as paleodepth changes during the Pliocene–Holocene.

In the near-seafloor samples, 44 ostracode species belonging to 29 genera were identified in Hole U1353B, and 51 species belonging to 34 genera were identified in Holes U1351A and U1351B. The dominant taxa in all three samples are Argilloecia spp. (U1353B = 9.8%; U1351A = 11.5%; U1351B = 19.5%), Hemicytherura gravis (U1353B = 4.1%; U1351A = 9.7%; U1351B = 9.6%), and Munseyella brevis (U1353B = 9.5%; U1351A = 7.9%; U1351B = 3.9%). In the sample taken from near the seafloor in Hole U1352B on the continental slope, the dominant taxon is Bairdoppilata sp. 1 (22.6%), which is present in small amounts (<3%) in samples taken near the bottom of the shelf sites.

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