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doi:10.2204/iodp.proc.322.103.2010

Biostratigraphy

Preliminary shipboard analysis of the core catcher and additional samples from Cores 322-C0011B-1R through 61R reveals assemblages of calcareous nannofossils and planktonic foraminifers (Tables T8, T9). Biostratigraphic datums were mainly derived from coccoliths (Fig. F34). According to these datum events, the composite of Hole C0011B has a middle–late Miocene age.

Floral and faunal assemblages of planktonic organisms provide some insight into paleoceanographic conditions. Species abundance is generally common to rare. In the late Miocene, sediments contain warm-water genera such as the calcareous nannofossil genus Discoaster.

Calcareous nannofossils

Preliminary examination of all core catcher samples from Hole C0011B obtained moderately to poorly preserved nannofossils, which occur in common abundance in most of the samples, and species diversity is comparatively high. However, severe dissolution occurred, leading to barren or very poor occurrence of coccoliths in some intervals (Table T8). Most of the zonal markers of Martini's zonation (1971) and Raffi et al. (2006) were identified in the sedimentary sequence. The nannofossils that occurred in Hole C0011B are listed in Table T8, and correlations between the hole and the biostratigraphy are shown in Figure F34 and Table T10.

Discoaster quinqueramus and Discoaster berggrenii, which indicate upper Miocene Zone NN11 (5.59–8.52 Ma), were found in Samples 322-C0011B-1R-CC through 9R-CC. The paracme beginning (PB) (Raffi et al., 2006) of Reticulofenestra pseudoumbilicus (8.78 Ma) was also identified in Samples 322-C0011B-9R-CC and 10R-CC. Discoaster hamatus, which appears between 10.541 and 9.56 Ma and is contrasted to Zone NN9, was found in Samples 322-C0011B-21R-CC through 24R-CC. The first occurrence (FO) of Catinaster coalitus, which shows the bottom of Zone NN8 (10.88 Ma), was recognized between Samples 322-C0011B-25R-5, 8–10 cm, and 26R-7, 103 cm. Samples 322-C0011B-26R-7, 10 cm, through 37R-CC are characterized by the sporadic occurrence of Discoaster kugleri and Coccolithus miopelagicus, which reveals that the intervals are assigned to Zone NN7 (between 10.88 and 11.90 Ma). Cyclicargolithus floridanus indicates the upper part of Zone NN6 (12.037 Ma) and was found below Sample 322-C0011B-39R-5, 43–43.5 cm. Therefore, the middle/late Miocene boundary is situated between Samples 322-C0011B-37R-CC and 38R-3, 127 cm. Sphenolithus heteromorphus disappeared at the Zone NN5/NN6 boundary (13.532–13.654 Ma) in the middle part of the middle Miocene, which lies between Samples 322-C0011B-53R-CC and 57R-CC. Eight nannofossil datums in Hole C0011B (from the FO of D. berggrenii to the last occurrence [LO] of S. heteromorphus) were at much higher levels compared to Sites 1173 and 1177. Calcareous nannofossil results for Hole C0011B and Sites 1173 and 1177 show biostratigraphic changes from the middle–late Miocene. However, calcareous nannofossil assemblages at Sites 1173 and 1177 were affected by both strong overgrowth and etching (Shipboard Scientific Party, 2001a). Better correlation of each datum event and the correct position of datum events require postcruise studies on additional samples from these core sections.

Planktonic foraminifers

Preliminary analyses of all core catcher samples from Cores 322-C0011B-1R through 61R and a few additional samples were examined on board the ship. Planktonic foraminifer fossils occurred in poor abundance with moderate to good preservation. Hole C0011B sediment samples have shown the planktonic foraminifer assemblages are barren to very rare in abundance in an almost consecutive number of intervals (Table T9).

Three biohorizons and datum events were noted from Hole C0011B (Table T9). The upper part of Unit II characterizes two biohorizons from core catcher Samples 322-C0011B-6R-CC, 7.5–12.5 cm, and 7R-CC, 11.5–16.5 cm, with the FO of Truncorotalia crassaformis and LO of Globoturborotalita nepenthes. The third and last biohorizon occurred during the upper part of Unit IV and was recognized by the LO of Catapsydrax dissimilis. A better evaluation of the rare availability and the correct position of datum events require postcruise studies on additional samples from the core sections.

Sedimentation rate

The sedimentation rate of calcareous nannofossils in Hole C0011B, which is categorized by three sections, is shown in Figure F35. The sedimentation rate for Unit II to the upper part of Unit III (421–497 m CSF) has been calculated at ~9.05 cm/k.y. In contrast, the sedimentation rate of the upper to middle part of Unit III (497–537 m CSF) decreased to 4.31 cm/k.y. Below 537 m CSF, the sedimentation rate remained stable and increased to 9.02 cm/k.y. from the lower part of Unit III to Unit IV.

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