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doi:10.2204/iodp.proc.340.109.2013

Paleontology and biostratigraphy

Core catcher samples from Site U1399 contain calcareous nannofossils and planktonic and benthic foraminifers of varying abundances and at varying levels of preservation. Calcareous nannofossil and planktonic foraminiferal data both indicate ages within the late Pleistocene (Fig. F2), suggesting extremely high sedimentation rates. Reworking of much older (early Pleistocene and late Pliocene) material is evident in several samples. Many of the core catcher samples from Site U1399 consist of very coarse grained material containing numerous shallow-water benthic foraminifers and fragments of shell and coral. Well-preserved pteropod and heteropod shells, otoliths, and sponge spicules (Demospongiae) were also found in some hemipelagic samples, notably Sample 340-U1399-3H-CC.

Calcareous nannofossils

A total of 20 core catcher samples from Hole U1399A and 14 from Hole U1399B were analyzed for nannofossil content; the samples contain an upper Pleistocene species assemblage. Calcareous nannofossils at the top of both holes are generally well preserved and abundant. At the base of both holes, the coarse sediment was unsuitable for nannofossil analysis. Samples 340-U1399A-1H-CC to 17H-CC yielded an abundant upper Pleistocene assemblage of Gephyrocapsa oceanica, Gephyrocapsa parallela, Helicosphaera hyalina, and Emiliania huxleyi. Therefore, these samples were assigned to Zone CN15 (Okada and Bukry, 1980). Early Pleistocene and early Pliocene reworked species were found along with a species assemblage belonging to Zone CN15 with a maximum age of 0.25 Ma (Kameo and Bralower, 2000).

In Samples 340-U1399A-20H-CC to 36X-CC (the base of Hole U1399A), an assemblage similar to the one found at the top of Hole U1399A (Samples 1H-CC to 17H-CC) was found. The presence of Ceratolithus cristatus with the absence of E. huxleyi indicates this section should be assigned to Subzone CN14b (Okada and Bukry, 1980). The same group of reworked species was found at the top and near the base of Hole U1399A. Hole U1399B shows a similar upper Pleistocene assemblage with reworked species from the early Pleistocene and Pliocene. C. cristatus is abundant in Sample 340-U1399B-6H-CC (more abundant than in any other sample). In Sample 340-U1399B-17H-CC, an early Paleocene species, Biantholithus sparsus, was found, suggesting multiple sources of the reworked sediments.

Planktonic foraminifers

Of the 36 core catcher samples from Hole U1399A, 33 were analyzed for planktonic foraminiferal content, along with 25 of the 27 core catcher samples from Hole U1399B. The remaining cores either did not contain any material or contained material too coarse for planktonic foraminiferal analysis. Planktonic foraminifers were present in all samples analyzed, although many of the samples contained extremely low abundances, possibly due to the high volume of volcanic material. In samples with abundant specimens, the assemblage of planktonic foraminifers was diverse but dominated by Globigerinoides ruber (white and pink), Globigerinoides sacculifer, and Neogloboquadrina dutertrei (dextral). Other abundant species include Globorotalia truncatulinoides and Globorotalia tumida. The assemblage does not change significantly throughout Site U1399, and all species present are indicative of warm subtropical waters.

Several datum species were found in both holes; however, reliable datum species were generally not found in samples with low planktonic foraminiferal abundance. Globorotalia flexuosa (0.07–0.40 Ma) and Globigerinella calida (bottom occurrence at 0.22 Ma) were only found in low numbers. The last occurrences of these datum species are not clearly defined, and no reliable planktonic foraminiferal datum was found at the base of either hole.

Several reworked coarse-grained samples from Holes U1399A and U1399B also contained datum species from the early Pleistocene and late Pliocene. Heavily abraded individuals of Globorotalia tosaensis (top occurrence [T] at 0.61 Ma) were found in a number of samples from Hole U1399A and in one sample from Hole U1399B. Specimens of Globorotalia exilis (T 2.10 Ma) and Globorotalia miocenica (T 2.39 Ma) were found in Samples 340-U1399A-9H-CC and 28X-CC and 340-U1399B-8H-CC and 9H-CC. Specimens of Dentoglobigerina altispira (T 3.13 Ma) and Sphaeroidinellopsis seminulina (T 3.16 Ma) and an abraded possible representative of Globigerinoides mitra (early to late Miocene) were also found in Samples 340-U1399B-10H-CC, 340-U1399A-34X-CC, and 340-U1399B-17H-CC, respectively.

Because these early Pleistocene and older species co-occur with late Pleistocene datum species G. calida and G. flexuosa, they cannot indicate the true age of the sediment but instead indicate the age of the sediment found within likely mass-flow deposits.

Benthic foraminifers

A total of 34 genera and 23 species were identified at Site U1399 in the >150 µm size fraction. Benthic foraminifers examined in Holes U1399A and U1399B varied in abundance, diversity, and preservation (poor to moderate). Hole U1399A has 18 species present, and Hole U1399B has 15. Rotaliids have low diversity and are present in low abundances (1–10 sediments per sample) overall in Holes U1399A and U1399B. Several samples (18) contain noticeable amounts of Amphistegina (1–30 specimens per sample), Cibicides wuellerstorfi (1–10 specimens per sample), and Melonis sp. (1–10 specimens per sample). Amphistegina sp. is common in reef environments (≤100 m depth), and their poor preservation within these samples is indicative of reworking consistent with volcaniclastic sedimentation in the area. Miliolids are present, with Pyrgo murrhina and Quinqueloculina granulocostata the dominant species in the uppermost six core catcher samples in both Holes U1399A and U1399B. Agglutinated foraminifers are extremely rare, with only Sigmoilopsis sp. present. Benthic foraminiferal abundance was low at Site U1399, ranging between 1 and 49 benthic foraminifers/g of sediment, with the exception of Sample 340-U1399A-4H-CC, which has an abundance of 92 benthic foraminifers/g of sediment.

The lack of dominant species in most samples, as well as the obvious influx of reef material, makes it challenging to provide a paleodepth estimate. However, C. wuellerstorfi is common in middle–lower bathyal to abyssal settings, whereas Pyrgo murrhina is common in middle to lower bathyal areas in the Grenada Basin (Galluzzo et al., 1990). Based on their very similar relative abundances and lack of other abyssal key taxa, a bathyal paleodepth is interpreted for the entire sampled interval.

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