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doi:10.2204/iodp.proc.324.104.2010

Paleontology

Sediments from Site U1347 (Cores 324-U1347A-1W through 11R) are generally carbonate-poor in lithology and comprise bioturbated siltstones and sandstones (stratigraphic Units II and III) with overlying chert and chalk fragments (stratigraphic Unit I) (see "Sedimentology"). Shipboard calcareous microfossil studies were performed on Unit II and III sediments (mudstones only for foraminifers) as well as on chalks from Unit I. Further, investigations of calcareous microfossils were extended into the underlying basement basaltic lava section, in which interbedded mudstones occurred at several levels (Units VI, VIII, XI, and XIII).

In general, calcareous nannofossils and foraminifers of Units I–III are moderate to poor in preservation and low in abundance and diversity. Intercalated sediments in the underlying basement section are almost barren of both microfossil taxa. Fortunately, the ages of four samples from Cores 324-U1347A-2R and 10R (Units I–III) are assignable to the Berriasian–Valanginian based on calcareous nannofossils. The foraminifer assemblage is marked by the absence of a planktonic group. Though the total number of specimens is limited, benthic foraminifers obtained from Units I–III most likely represent a neritic assemblage (Cores 6R through 8R) and subsequent bathyal faunal elements upsection (Cores 1R and 2R). Therefore, an overall deepening trend from <200 mbsl (Unit III) to 200–2500 mbsl (Unit I) is inferred (note lack of foraminifer data for Unit II).

Washed foraminifer samples are to a large extent dominated by volcanogenic lithic fragments and minerals. Radiolarians consistently occur throughout the sediment and basement sections, with peaks in size, abundance, and diversity in Cores 6R through 8R. A highly abundant, diverse radiolarian assemblage is observed in Sample 324-U1347A-13R-7, 19.5–21.5 cm (Fig. F14).

Calcareous nannofossils

Calcareous nannofossils in the sediments of Site U1347 are moderately preserved and occur in high abundance in the topmost interval (Unit I). Preservation declines to poor and abundance decreases to rare around Core 324-U1347A-324-6R and further downhole. The sediments recovered from between the underlying basaltic units are barren of calcareous nannofossils.

The presence of zonal marker species Cruciellipsis cuvillieri together with Axopodorhabdus cylindratus, Cretarhabdus striatus, and Speetonia sp. allows for the assignment of stratigraphic Unit I (Sample 324-U1347A-2R-1, 12 cm; encrusting limestone on a chert piece) to the Berriasian to Aptian (see "Paleontology" in the "Methods" chapter; Bown, 2005). Of these taxa, C. striatus is assumed to be a contaminant from RCB drilling, which often causes soft-sediment mixing. Hence, the proposed biostratigraphic range of Sample 324-U1347A-2R-1, 12 cm, is from Zone NK1 to Subzone NK3b (Berriasian–upper Valanginian) (Table T4). Likewise for Unit III, the presence of C. cuvillieri together with A. cylindratus (Samples 324-U1347A-6R-2, 97 cm; 7R-3, 65 cm; and 10R-1, 66 cm) indicates a biostratigraphic range from Zone NK1 to Subzone NK3b (Berriasian–upper Valanginian) (Table T4).

It should be noted that the majority of examined samples show a low-diversity assemblage, which is often solely composed of Watznaueriaceae occasionally together with the small proportion of Chiastozygazeae (Core 324-U1347A-3R through Section 6R-1, Sections 7R-CC through 9R-1, and Cores 10R through 17R [except for Sample 324-U1347A-10R-1, 66 cm]). The absence of primary zonal marker species in these intervals hinders the chronostratigraphic interpretation.

The above-described calcareous microfossil zonation translates to a numerical age interval of 140–133 Ma for Units I–III. Accordingly, the estimated age of the basaltic basement section immediately below would be 140–133 Ma or older.

Foraminifers

Foraminifer abundance and diversity are low through the examined interval at Site U1347. No planktonic foraminifers were encountered during the course of shipboard study, as was the case at Site U1346. Benthic foraminifer specimens exhibit good to moderate preservation, and they tend to be broken or fragmented with increasing burial depth (Table T5).

Though present only in trace amounts, benthic foraminifers recorded from stratigraphic Unit I belong to the genera Dorothia, Glomospirella, and Ramulina (Table T5). In general, these taxa are ubiquitous in the bathyal setting (200–2500 mbsl) (e.g., Sliter and Baker, 1972; Koutsoukos and Hart, 1990; Holbourn et al., 2001).

Downhole, Unit III yields such benthic foraminifer genera as Dentalina, Lenticulina, Planularia, and Conorboides. The former three are nodosariids and the same faunal elements as those of the Site U1346 assemblage at the neritic–upper bathyal depth (largest number of specimens collected from Sample 324-U1347A-7R-4, 50–52 cm). The occurrence of Conorboides (Sample 324-U1347A-8R-2, 49–51 cm) is important, as its Cretaceous bathymetric distribution is considered to have been narrowly restricted to the neritic setting (e.g., Koutsoukos and Hart, 1990; Jones and Wonders, 1992). Taking into account the lack of taxa typical of the bathyal setting, the water-depth estimate for Unit III is most likely <200 mbsl, though further effort to increase the number of specimens is critical.

Several intercalated mudstone layers in the basaltic basement section (stratigraphic Units VI, VIII, XI, and XIII) are almost barren of foraminifers, although they all disaggregate well by means of the kerosene method (see "Paleontology" in the "Methods" chapter). Two levels (Samples 324-U1347A-15R-1, 70–72 cm, and 17R-1, 41.5–43.5 cm) are marked by a few small and/or fragmented specimens of nodosariid benthic foraminifers, which are difficult to interpret in terms of paleowater depth.

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