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doi:10.2204/iodp.proc.320321.212.2013

Results

Hole U1331C

A total of 29 benthic foraminiferal taxa were recognized (Table T1). Preservation of benthic foraminifers at Site U1331 is poor due to diagenesis caused by circulation of pore waters through the underlying basalt. Calcareous forms were poorly preserved, with recrystallized walls. The number of foraminifers per gram of sediment ranges from 1 to 7, very low numbers compared to normal deep-sea sediments. Foraminifers that do not use carbonate to agglutinate such as Ammovertellina prima, Thalmannammina conglobata, Paratrochamminoides olszewskii, and Cyclammina elegans occurred mainly in the lower samples studied. It is not clear whether these forms are present because of the shallow CCD or because of local influences. The East Pacific CCD in the early Eocene was located at a relatively shallow depth of 3000–3500 m. The early Eocene paleodepth of Site U1331 was near this CCD but was slightly above the CCD (Pälike et al., 2009).

The most common calcareous forms, Nuttallides truempyi, Oridorsalis umbonatus, Anomalinoides spissiformis, and Quadratobulimina pyramidalis, appeared only in the uppermost sample studied. This assemblage is similar to the normal deep-sea assemblage in the early to early middle Eocene, although it has very low species richness.

Hole U1333A

A total of 79 foraminiferal taxa were recognized in this hole (Table T2). The preservation of benthic foraminifers was generally moderate, with recrystallization of the walls in the lower samples, but poor preservation and corroded walls as well as low abundance in the upper interval from Samples 320-U1333A-16X-1, 24–27 cm, through 16X-4, 75–77 cm. The absolute abundance (number of foraminifers per gram of sediment) fluctuates, being higher in the two higher intervals from Samples 320-U1333A-16X-6, 75–77 cm, to 17X-5, 75–77 cm, and 19X-3, 125–127 cm, to 20X-3, 25–27 cm. The former yields 12.9 individuals per gram, and the latter yields 31.8 individuals per gram. A distinct decrease in species number is recognized between Samples 320-U1333A-16X-5, 75–77 cm, and 16X-6, 75–77 cm, decreasing from 27 to 11 taxa. In general, the number of foraminifers per gram of sediment is negatively correlated with the abundance of radiolarians and positively correlated with the carbonate content, with highest numbers during the middle Eocene carbonate accumulation events (CAE 2–3). The species diversity changes from 3.0–4.0 to 0.7–3.0 and the species equitability changes from 0.5–0.6 to 0.7–0.9 between samples with low and high carbonate content. Although a distinct change in species diversity and equitability occurred, the main constituents of the assemblage did not change, suggesting that the decreased abundance is due to dilution with radiolarians rather than dissolution. Agglutinated foraminifers were common in abundance.

The most common species are Karreriella subglabra, Spiroplectammina spectabilis, Abyssamina quadrata, Alabamina dissonata, A. spissiformis, Cibicidoides eocaenus, Cibicidoides grimsdalei, Gyroidinoides girardanus, N. truempyi, O. umbonatus, Siphonodosaria aculeata, pleurostomellids, and species of Pullenia.

Hole U1333B

A total of 67 taxa were recognized in the nine samples studied from Hole U1333B (Table T3). The assemblage in Samples 320-U1333B-20X-1, 73–75 cm, to 20X-2, 73–75 cm, is similar to that recognized in Samples 320-U1333A-19X-4, 25–27 cm, to 20X-1, 25–27 cm, with abundant foraminifers per gram of sediment. In general, the preservation is moderate to poor, and specimens have recrystallized walls.

The foraminiferal species are similar to these in Hole U1333A, including C. grimsdalei, C. eocaenus, A. dissonata, A. quadrata, A. spissiformis, G. girardanus, N. truempyi, O. umbonatus, and nodogenerinids. Most have large tests with thick walls. The assemblage shows a similar level of species diversity, 3.0–4.0, and similar levels of species equitability, 0.5–0.7.

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