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doi:10.2204/iodp.proc.336.104.2012 MicropaleontologySeveral layers of interbasalt sediments were encountered in Core 336-U1382A-8R. Sediments comprise all of Sections 336-U1382A-8R-2 and 8R-3 and are calcareous nannofossil ooze. In Section 336-U1382A-8R-4, consolidated ooze occurs from 6 to 27 cm, and a polymictic breccia extends from 31 to 42 cm. Smear slides show abundant calcareous nannofossils throughout these sediments (Table T9; Figs. F29, F30). The common to abundant species in the sediment sections are short-ranged Discoaster quinqueramus (NN11), in addition to longer ranging Discoaster brouweri (NN9–NN18) and Discoaster variabilis (NN9–NN16). The conjunction of D. quinqueramus and D. brouweri is assigned to the upper Miocene Discoaster quinqueramus Zone (NN11). The absence of Amaurolithus spp. or Amaurolithus primus may indicate Subzone NN11A, which has an approximate age bracket between 7.2 and 8.5 Ma, according to the Neogene nannofossil biostratigraphic zonation of Bown (1998; fig. 8.1, p. 227). More or less similar age data were assigned to basement at Site 395 (Melson, Rabinowitz, et al., 1979), which is located only 50 m east of Hole U1382A. Site 395 is in oceanic crust magnetized during magnetic Anomaly 4 (Shipboard Scientific Party, 1979), estimated to be ~8 Ma on the basis of the revised geologic timescale of Walker and Geissman (2009). The 40Ar/39Ar age dating from feldspars of one crustal core sample at Site 395 shows an age of 9.8 Ma ± 2.9 m.y. (Turner et al., 1979). The basal sediment at Site 395 belongs to the upper Miocene Amaurolithus primus Subzone (NN11B, Messinian) of the Discoaster quinqueramus Zone (Bukry, 1979; Bown, 1998). The discoasters, which are the most abundant nannofossils in the sediments, are subtropical species and may indicate the climate of this region during deposition in the late Miocene. Other microfossil groups, like foraminifers and radiolarians, are very rare (Table T9). All of the foraminifers observed are planktonic (Globorotalia spp. and others), and they are altered or mineralized (Fig. F30). The radiolarians are too fragmented or dissolved to identify species (Fig. F30C). Only a single dinoflagellate specimen was identified in one sample (Sample 336-U1382A-8R-4, 24–25 cm; Fig. F30D). |
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