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doi:10.2204/iodp.proc.324.103.2010

Paleontology

Sediments from Site U1346 (Cores 324-U1346A-1W through 6R) are lithologically variable (stratigraphic Units I–IV; see "Sedimentology") and more or less lithified, yet relatively unconsolidated marly/chalky portions are present in Units III (calcareous mudstones/sandstones) and IV (limestones). These levels were chosen for shipboard calcareous microfossil studies. In addition, calcareous nannofossils were investigated for such lithologies as carbonate-poor sandstones (Unit IV) and chert-encrusting limestones (Unit II).

Lower Cretaceous (Berriasian–Hauterivian) calcareous nannofossils with moderate to poor preservation were retrieved from most of the examined levels in Cores 324-U1346A-2R through 6R irrespective of the lithologic differences (stratigraphic Units II–IV). Foraminifers were obtained from the marly lithology of Section 324-U1346A-4R-CC, although the planktonic group was completely absent. Accordingly, the primary biostratigraphic age control for Site U1346 sediments was developed solely using the nannofossil assemblage analysis. Benthic foraminifers from Section 324-U1346A-4R-CC were well preserved and diverse, predominantly from the neritic–upper bathyal assemblage (estimated paleodepth ≤500 mbsl).

Various biogenic sedimentary components were observed in the samples processed for foraminifer analyses, which are predominantly radiolarians (recrystallized to calcite) and subordinately ostracodes, inoceramid prisms, echinoid plates, sponge spicules, bryozoans, and carbonaceous fragments (presumably of terrestrial higher plant origin). Noteworthy is the presence of articulated ostracodes indicating autochthonous burial.

Calcareous nannofossils

Calcareous nannofossils in the sediments from Site U1346 are rare to abundant and moderately to poorly preserved. All stages of overgrowth and etching were found.

The uppermost part of the sediments (Unit I) is represented by black chert pieces encrusted by limestone to a small extent. This limestone (Sample 324-U1346A-2R-1, 1 cm) contains Cruciellipsis cuvillieri (Fig. F9A, F9B), and Speetonia sp. (Fig. F9C, F9D), as well as Cretarhabdus striatus, which implies a mixture of calcareous nannofossil taxa of the entire Cretaceous (Berriasian–Maastrichtian) (Table T3) within the sample. In contrast, a considerable number of well-preserved coccospheres (Fig. F9E, F9F) are observed in Sample 324-U1346A-2R-CC, 1 cm (chert pieces), which points to autochthonous deposition. The limestone of Unit II contains a small number of poorly preserved Watznaueriaceae, for which age determination is not possible as they occur through the entire Cretaceous. Beneath, a graded sequence (interpreted as turbiditic in origin) of Unit III contains a nannofossil assemblage that again ranges through the entire Cretaceous (Samples 324-U1346A-4R-2, 27–30 cm, and 4R-2, 107–108 cm) (Table T3).

In the underlying clay-rich limestone of Unit IV, the occurrence of Eprolithus antiquus allows the assignment of Sample 324-U1346A-4R-2, 140 cm, to Subzone NC4a (early Hauterivian) (Table T3; see "Paleontology" in the "Methods" chapter), whereas Sample 4R-CC, 3 cm, indicates an Early Cretaceous range (Table T3). The next fossiliferous sample below is a shell-rich limestone bed (Sample 324-U1346A-5R-1, 53–54 cm) (Table T3) that yields Rotelapillus laffittei (Fig. F9G, F9H). Based on the nannofossil assemblage the age of this sample is assignable to Subzones NK2a to NC5a–NC5b (Berriasian–early Hauterivian). This assignment is consistent with the occurrence of E. antiquus (Subzone NC4a; early Hauterivian) in Sample 324-U1346A-5R-CC, 24–25 cm. The lowermost Sample 324-U1346A-6R-1, 24–25 cm, yields a large number of heavily overgrown Watznaueriaceae, which again prevents accurate age determination.

In summary, the age of the middle–lower part of stratigraphic Unit IV (Samples 324-U1346A-5R-1, 53–54 cm, to 6R-1, 23 cm) is most likely 142–128 Ma (the base of Subzone NJKd to the base of Zone NC5). This indicates that the age of basement basalts is 142–128 Ma or older.

Foraminifers

Well-preserved foraminifers with hollow tests were successfully obtained from two marly samples (324-U1346A-4R-CC, 3–4 cm, and 4R-CC, 7–8 cm); four other examined samples were indurated and/or not sufficiently disaggregated (Table T4).

The foraminifer assemblage is characterized by the complete lack of planktonic foraminifers, even in the finer 63–150 µm sediment fraction. Two explanations are possible for this observation: (1) the examined levels are pre-Aptian in age (as deduced from the calcareous nannofossil zonation), prior to the major planktonic foraminifer evolution in terms of abundance, diversity, and test size; and/or (2) the overwhelmingly large population of radiolarians induced an ecological bias in the zooplankton community.

Benthic foraminifers are diverse and comprise the neritic to upper bathyal assemblage (Table T4). Ten calcareous genera were identified: Dentalina, Laevidentalina, Frondicularia, Lenticulina, Saracenaria, Astacolus, Vaginulinopsis, Citharina, Planularia, and Psilocitharella. These genera are all placed under the family Nodosariidae according to Loeblich and Tappan (1988). Bolli et al. (1994) and Holbourn and Kaminski (1997) attributed the latter seven genera to the family Vaginulinidae. The nodosariids (or nodosariids and vaginulinids) have been known to dominate in the neritic to upper bathyal setting (e.g., Sliter and Baker, 1972; Sliter, 1977; Koutsoukos and Hart, 1990). Accordingly, the estimated paleodepth for stratigraphic Unit IV (see "Sedimentology") of Site U1346 is ≤500 mbsl.

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