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doi:10.2204/iodp.proc.329.105.2011

Paleontology and biostratigraphy

At Site U1367, we recovered a ~24 m thick sequence of clay-bearing nannofossil ooze with foraminifers at the bottom, nannofossil ooze with foraminifers in the middle, and metalliferous pelagic clay at the top spanning from the base of the Oligocene to the present (Fig. F17; see also “Lithostratigraphy”). See the “Appendix” for a list of foraminifer and ostracod taxa.

Five core catcher samples from the base of Cores 329-U1367C-1H (at 7.2 mbsf), 329-U1367B-2H (at 13.42 mbsf) and 3H (at 21.9 mbsf), 329-U1367E-3H (at 24.3 mbsf), and 329-U1367C-3H (at 24.9 mbsf) were examined for paleontological and biostratigraphic purposes using the >63 µm sediment size fraction. The three deeper samples are dominated by planktonic foraminifers, with lesser amounts of benthic foraminifers and ostracods (i.e., Sample 329-U1367-2H-CC in Fig. F18). The biogenic component of the fine fraction (<63 µm) is dominated by nannofossils (see “Lithostratigraphy”). The preservation of the different calcareous microfossil groups ranges from moderate near the bottom (Sample 329-U1367B-3H-CC) to very good in the middle of the sequence (Sample 2H-CC) to poor at the base of Core 329-U1367C-1H. The good carbonate preservation between ~24 and 13.4 mbsf may be due to the shallow depth of the Site U1367 seafloor relative to the calcite lysocline in the early Oligocene. The decrease in preservation near the top is probably due to sinking of the aging seafloor relative to the lysocline followed by sinking of the seafloor beneath the calcite compensation depth (CCD) at the transition from carbonate ooze to pelagic clay. This carbonate preservational history is also reflected in the deepwater environment by the relatively high abundance and excellent preservation of the benthic calcareous microfossils.

Planktonic foraminifers

Biostratigraphic assignments for Site U1367 are derived from planktonic foraminifers. The overall assemblage includes Globigerina euapertura, Globigerina pseudovenezuelana, Subbotina eocaena, Subbotina linaperta, Subbotina gortanii, Globigerina tapurensis, Globigerina praebulloides, Chiloguembelina cubensis, Cassigerinella chipolensis, Cassigerinella sp., Catapsydrax disimilis, Tenuitellinata angustiumbilicata, Tenuitellinata gemma, Paragloborotalia opima nana, Paragloborotalia opima opima, Pseudohastigerina micra, and Pseudohastigerina naguewichiensis (Table T4). These species are characteristic of Oligocene fauna in low and mid-southern latitudes (Bolli et al., 1985; Jenkins, 1985; Leckie et al., 1993; Berggren and Pearson, 2005; Wade et al., 2007, 2011). We noted the highest diversity of Oligocene taxa, 13 species, in Sample 329-U1367B-2H-CC. Although the stratigraphic distribution of some of the species found at Site U1367 extends into the late Eocene, none of the diagnostic late Eocene forms, such as Hantkenina spp., Turborotalia cerroazulensis, and Globigerinatheka spp., were found.

The lowermost samples examined (Table T4) from ~24 mbsf are inferred to correspond to the boundary between planktonic foraminifer Zones O1 and O2 (~32 Ma) based on the last occurrence (LO) of P. naguewichiensis and S. eocaena (Berggren et al., 1995; Wade et al., 2011) and the presence of P. micra. The LO of P. micra has been established at ~32.2 Ma (Pearson et al., 2006). Sample 329-U1367B-2H-CC (13.4 mbsf) is inferred to correspond to planktonic foraminifer Zones O3/O4 (30.6–29.4 Ma) based on the common occurrence of C. cubensis and Paragloborotalia opima (Pearson et al., 2006; Wade et al., 2011). It was not possible to assign the uppermost sample examined at ~7.2 mbsf to a biostratigraphic zone because planktonic foraminifers were poorly preserved. Postexpedition shore-based examination will be required to refine the foraminifer biostratigraphy at this site.

Benthic foraminifers

More than 18 species of benthic foraminifers were observed in the five samples examined from Site U1367. The assemblage was of relatively high diversity (11–16 species) in the upper two samples (Cores 329-U1367B-2H and 329-U1367C-1H) and showed a marked decline (to 3 species) at the bottom of the section. The overall benthic foraminifer assemblage includes Cassidulina subglobosa, Cibicidoides sp., Dentalina ariena, Dentalina sp., Gyroidinoides soldanii, Karreriella chapapotensis, Lagena spp., Lenticulina gibba, Nodosaria spp., Nuttalides umbonifer, Oridorsalis umbonatus, Pleurostomella sp., Siphonodosaria antillea, Siphonodosaria spinata, Textullaria sp., and Vulvulina spinosa. Only K. chapapotensis and Nodosaria sp. are present throughout the entire section (Table T5).

Ostracods

Sixteen ostracod genera were found in the core catcher samples from Site U1367 (Table T6). Maximum diversity was observed in Sample 329-U1367B-2H-CC (13.4 mbsf) and the lowest diversity (two genera) at the shallowest (7.2 mbsf) and deepest (>24 mbsf) parts of the site. Ostracod preservation ranged uniformly with overall abundance, ranging from very good (several articulated specimens present) to moderate (fragmented valves). Ostracods were preliminarily identified to the generic level and consist of genera that have worldwide distribution and are common in Cenozoic deep-sea sediment (Ayress et al., 1997; Dingle and Lord, 1990; Cronin et al., 2002). Sample 329-U1367B-2H-CC mainly contained Krithe, Hemiparacytheridea, Poseidonamicus, Bradleya, Cytheropteron, and Henryhowella. Krithe and Argilloecia were dominant at the base of the sedimentary section, near the sediment/basement interface, whereas Krithe and Henryhowella were the only genera present in the uppermost sample (Table T6).

Krithe and Argilloecia are common genera in the cold, organic-rich deep-sea North Atlantic (Coles et al., 1994; Rodriguez-Lázaro and Cronin, 1999). In contrast, Bradleya and Henryhowella have been found associated with well-oxygenated deep-sea environments (Cronin et al., 1999; Didié and Bauch, 2000; Alvarez Zarikian et al., 2009).

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