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doi:10.2204/iodp.proc.334.105.2012

Paleontology and biostratigraphy

At Site U1380, samples taken from 400–480 mbsf were analyzed for calcareous nannofossils and foraminifers. Calcareous nannofossils provide biostratigraphic control for this section (Table T2). The sediments of the deepest recovered core were tentatively estimated to be lower Pleistocene. Planktonic foraminiferal zones were not established because of the rare occurrences of planktonic foraminifers. Benthic foraminifers reflect continuous, alternating paleoenvironmental changes from an upper to a middle slope environment.

Calcareous nannofossils

Lower Pleistocene Zone NN19 is observed in the core catcher samples recovered from Hole U1380A. However, the top and bottom boundaries of this zone, defined by the last occurrence of biostratigraphic markers Pseudoemiliania lacunosa and Discoaster brouweri, respectively, cannot be constrained. With the exception of barren Sample 334-U1380A-7R-CC (452.64 mbsf), calcareous nannofossils occur consistently throughout the section in abundances from few to abundant. Preservation ranges from poor to moderate. Heavy mixing with terrigenous sediments occurs throughout the entire interval. The presence, abundance, and preservation of calcareous nannofossils are presented in Table T3.

Samples 344-U1380A-2R-CC (402.77 mbsf) through 10R-CC (479.73 mbsf) are assigned to Zone NN19 of the lower Pleistocene based on the presence of P. lacunosa and the absence of D. brouweri. The dominant species include Helicosphaera carteri, Helicosphaera sellii, Helicosphaera neogranulata/hyalina, Coccolithus pelagicus, and Calcidiscus leptoporus. Sample 7R-CC (452.64 mbsf) is barren of calcareous nannofossils.

Foraminifers

Generally, foraminiferal abundances are common or rare in the sediment of Hole U1380A. Foraminiferal preservation is moderate or poor, and diagenetically overprinted brown specimens were observed. These trends are similar to the lowermost part of nearby Site U1378. Planktonic foraminifers were analyzed in limited horizons of six core catcher samples (Table T4). Planktonic foraminifers are rare or very rare in this hole and are generally characteristic of tropical fauna such as Globigerinoides quadrilobatus (Globigerinoides sacculifer), Globigerinoides ruber, Orbulina universa, Globorotalia menardii, and Neogloboquadrina dutertrei. Because of the absence of the species commonly used as markers for planktonic foraminiferal biostratigraphy, no zones have been established.

Benthic foraminifers were analyzed in limited horizons of six core catcher samples (Table T2). Benthic foraminiferal abundances in the sediment are common or rare. In general, many of the species of benthic foraminifer observed in the cored sediment are similar to modern assemblages, which are characteristic of the oxygen-minimum zone (100–1000 mbsf) of the seafloor in this region. The detected faunas include many species similar to those of nearby Site U1378. Samples contain Bolivina argentea, Epistominella smithi, Uvigerina peregrina, Cibicidoides mckannai, and Gyroidina, which are characteristic of upper to middle bathyal (200–500 mbsl) paleoenvironments.

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