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doi:10.2204/iodp.proc.340.105.2013

Paleontology and biostratigraphy

Core catcher samples at Site U1395 contain calcareous nannofossils and planktonic and benthic foraminifers of varying abundances and at varying levels of preservation. Preservation deteriorates with depth, making the samples increasingly difficult to date. Both nannofossil and planktonic foraminiferal biostratigraphic data for Site U1395 suggest ages ranging from late Pleistocene to late Pliocene (Fig. F3). Biostratigraphic and paleomagnetic age determinations are in good general agreement (see “Paleomagnetism”). Sponge spicules, pteropods, and heteropods are abundant and generally well preserved in the upper samples. Otoliths are present throughout the core samples, and four different morphotypes are present. Ostracods are rare when present in Holes U1395A and U1395B.

Calcareous nannofossils

Of the 27 core catchers collected from Hole U1395A, 22 were analyzed for calcareous nannofossils, along with 18 of the 25 core catchers collected from Hole U1395B. The remaining samples were not analyzed because of the coarse nature of the material. Sample 340-U1395A-1H-CC yielded a characteristic Pleistocene assemblage with Geophyrocapsa oceanica, Rhabdosphaera clavigera, Gephyrocapsa muellerae, Helicosphaera kamptneri, Helicosphaera hyalina, and small (<3 µm) forms that may be Emiliania huxleyi. However, because of the small size of this species, postcruise analysis using scanning electron microscopy will be beneficial. Pseudoemiliania lacunosa was not found in Sample 340-U1395A-1H-CC, dating the sample to <0.289 Ma, Zone CN15 (Okada and Bukry, 1980).

Samples 340-U1395A-2H-6 to 11H-CC yielded a variety of gephyrocapsid species: P. lacunosa, Ceratolithus cristatus, H. hyalina, Calcidiscus leptoporus, R. clavigera, Calciosolenia murrayi, and Syracosphaera pulchra. The presence of G. oceanica indicates this sediment is within Subzone CN14b (Okada and Bukry, 1980) or the P. lacunosa Zone (Gartner, 1977). Large P. lacunosa specimens appear in Sample 340-U1395A-6H-CC, whereas G. oceanica starts diminishing in abundance in Sample 9H-CC. The preservation and abundance of these samples varies from good to poor and common to abundant, respectively, depending on the nature of the sediment in the core catcher. Generally, Samples 340-U1395A-2H-6 through 11H-CC show common to abundant species and good preservation. Samples 340-U1395A-12H-CC through 28X-CC show a lower Pleistocene assemblage with very small gephyrocapsids: Gephyrocapsa caribbeanica, P. lacunosa, C. leptoporus, and Crenalithus doronicoides. The latter was detected in Sample 340-U1395A-12H-CC, the first sample below the lowest occurrence of G. oceanica, indicating that this sediment is within Subzone CN13b (Okada and Bukry, 1980). Moreover, a high level of dominantly small Gephyrocapsa species was found, allowing placement within the small Gephyrocapsa Subzone (Gartner, 1977). The abundance of specimens within these samples ranges from barren (Samples 340-U1395A-17X-CC, 20X-CC, and 24X-CC) to abundant (i.e., Samples 340-U1395A-23X-CC and 28X-CC). Preservation ranges from moderate to good within this zone.

A similar lower to upper Pleistocene assemblage was recovered in Hole U1395B. Sample 340-U1395B-1H-CC contained a variety of gephyrocapsids, such as G. oceanica and Gephyrocapsa parallela. A high number (common) of Helicosphaera were also detected (H. hyalina, H. kamptneri, and Helicosphaera carteri var. walichii). C. cristatus and Ceratolithus telesmus were found to be common with good preservation. With the absence of both P. lacunosa and small calcareous forms, such as E. huxleyi, Sample 340-U1395B-1H-CC was assigned to Zone CN14.

Samples 340-U1395B-3H-CC to 16X-CC contain a similar species assemblage to the equivalent depth in Hole U1395A (S. pulchra, G. oceanica, G. caribbeanica, H. hyalina, R. clavigera, C. leptoporus, C. cristatus, Pontosphaera discopora, Pontosphaera multipora, and P. lacunosa). Large specimens of P. lacunosa were abundant in Sample 340-U1395B-5H-CC and were increasingly prevalent in Sample 12H-CC. Helicosphaera species, such as H. carteri, were abundant in Sample 340-U1395B-16X-CC. P. discopora and Pontosphaera japonica were common in Section 340-U1395B-10H-6. The overall preservation of species in these samples is good with no signs of dissolution or etching. These samples were assigned to Subzone CN14a (Okada and Bukry, 1980) or the P. lacunosa Zone (Gartner, 1977). Samples 340-U1395B-17X-CC to 25X-CC yielded a characteristic lower Pleistocene assemblage with high levels (common to abundant) of small Gephyrocapsa, P. lacunosa, G. caribbeanica, and C. doronicoides. G. oceanica was not present in Samples 340-U1395B-17X-CC to 25X-CC. As a consequence, these samples were assigned to Zone CN13b. The overall preservation of this zone is good; however, the abundance of species drastically decreases in Sample 340-U1395B-20X-CC because of the mixing of siliclastic fragments that were found within the sample. The lowermost Sample 340-U1395B-25X-CC shows a high prevalence (common) of H. carteri.

Planktonic foraminifers

Of the 28 core catcher samples from Hole U1395A, 27 were analyzed for planktonic foraminifers, as well as all 25 core catcher samples from Hole U1395B. Planktonic foraminifers were generally found to be the dominant presence in the >150 µm size fraction, except in samples with high volcanic content or very poor preservation. In most samples, the assemblage of planktonic foraminifers is diverse but dominated by Globigerinoides ruber (white) and Globigerinoides sacculifer. The assemblage of planktonic foraminifers throughout the site is typical of subtropical waters, with other abundant species including Globigerina falconensis, Globigerinita glutinata, Globigerinoides elongatus, Globorotalia tumida, and Neogloboquadrina dutertrei (dextral). Three biozones were recorded: PT1b, PT1a, and PL6. The primary marker between Subzone PT1a and Zone PL6 (top occurrence [T] of Globigerinoides fistulosus) was not recorded because of the absence of G. fistulosus at this location. Zone PL6 was recognized, instead, based on the presence of Globorotalia exilis, a secondary datum within Zone PL6, in the lowest sample from Hole U1395A. Several secondary datums were recorded as well: Globorotalia flexuosa (0.07–0.40 Ma), Globigerinella calida (bottom occurrence [B] at 0.22 Ma), Globorotalia tosaensis (T 0.61 Ma), and G. exilis (T 2.1 Ma). The bottom of Globorotalia truncatulinoides was recorded, but because of the roughly concurrent bottom of the related species G. tosaensis, this datum should be disregarded as a true age designation. The base of this species is likely abnormal at this site because of either ecological or preservational differences. It should be noted that within the lower sections of this site, samples become highly indurated and preservation deteriorates, making biostratigraphic designations less certain. Although this uncertainty is an issue, these age designations are based on the rough agreement between nannofossils and planktonic foraminifers.

Benthic foraminifers

A total of 57 genera and 49 species were identified at Site U1395 in the >150 µm size fraction. Samples examined for benthic foraminifers in Holes U1395A and U1395B varied in diversity and preservation (generally moderate). Rotaliids have the highest diversity but are present in low abundances (1–10 specimens per sample) overall in Holes U1395A and U1395B. Cibicides and Cibicidoides are the dominant genera, and Cibicides wuellerstorfi is the most abundant species. Miliolids have very low diversity and are present in low abundances with the exception of Pyrgo murrhina, the dominant species. Similarly, agglutinated foraminifers are represented by the genera Sigmoilopsis, Bigenerina, and Vulvulina, and Karreriella bradyi is the dominant species. Benthic foraminiferal density is low in both Holes U1395A and U1395B, ranging between 1 and 88 foraminifers/g of sediment.

At this site, Siphonodosaria cooperensis, Vulvulina pennatula, Pleurostomella alternans, and Proxifrons inaequalis are present in relatively low abundances (1–10 specimens per sample) in Samples 340-U1395A-8H-CC, 11H-CC, 12H-CC, 15H-CC, 18H-CC, 21H-CC, 22H-CC, and 26H-CC and 340-U1395B-20X-CC and 23X-CC. The last appearance datum (T) for this foraminiferal group is 0.58 Ma (Hayward et al., 2006). Based on the presence of the genus Osangularia and species Uvigerina auberiana, Laticarinina pauperata, and Bulimina aculeata, a bathyal paleodepth is interpreted.

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