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doi:10.2204/iodp.proc.317.106.2011

Biostratigraphy

Holocene to late early Pliocene biostratigraphy of Site U1354 was based on the shipboard study of calcareous nannofossils, diatoms, and planktonic and benthic foraminifers in core catcher samples from Holes U1354A–U1354C (Table T4; Fig. F13). Additional intracore samples were taken from selected cores to address specific age and paleoenvironmental questions using calcareous nannofossils. All microfossil groups were represented throughout the cored section except for diatoms, which were found only in a few Pleistocene samples. All depths in this section are reported in m CSF-A.

Holocene to Pleistocene sections from Samples 317-U1354A-1H-CC, 0 cm, through 19H-CC (3.78–85.38 m), 317-U1354B-1H-CC through 15H-CC (4.06–77.25 m), and 317-U1354C-2H-CC through 10X-CC (72.57–127.79 m) were primarily dated and divided into Zones NN21–NN19 using calcareous nannofossils. Two hiatuses were identified with nannofossil dating: (1) an intra-Pleistocene hiatus between Samples 317-U1354A-15H-CC and 17H-CC (76.20–80.16 m) and between 317-U1354B-15H-1, 15 cm, and 15H-1, 39 cm (73.65–73.89 m), where ~0.3 m.y. was missing, and (2) a hiatus at the base of the Pleistocene between Samples 317-U1354C-9X-CC and 10X-CC (122.20–133.37 m), where ~1 m.y. was missing. Another potential hiatus was identified on the basis of calcareous nannofossil dating and magnetostratigraphic data in Holes U1354A and U1354B at 69.90 and 64.75 m, respectively.

The Pliocene section between Samples 317-U1354C-10X-CC and 36X-CC (133.37–375.33 m) was poorly dated, but calcareous nannofossil and planktonic foraminifer biostratigraphy suggested an age of middle Pliocene (older than 2.78 Ma, calcareous nannofossils) to late early Pliocene (younger than 4.3 Ma, planktonic foraminifers). There was no biostratigraphic evidence for the late Pliocene, which was probably missing at the level of the Pleistocene–Pliocene hiatus.

Benthic foraminiferal abundances were generally indicative of subtidal to middle shelf depths throughout the Pleistocene, and planktonic foraminifers suggested that deposition occurred generally under sheltered, inner neritic conditions with short-lived excursions to outer neritic and extraneritic conditions. Pliocene deposition occurred generally at inner shelf water depths (and possibly middle shelf depths) under sheltered, inner neritic conditions.

Calcareous nannofossils

Nannofossil assemblages at Site U1354, located on the outer shelf, were typically common to abundant and moderately to well preserved (Table T5). The Pleistocene succession was robustly dated by nannofossil biostratigraphy (Table T4). Although standard zonal markers were absent for the Pliocene section, the Reticulofenestra lineage provided crude, though critical, age control for this interval.

Holocene–Pleistocene

Although not identified biostratigraphically, the base of the Holocene was tentatively placed at Section 317-U1354A-2H-1, 25 cm (4.03 m), where there was a distinct lithologic change between greenish gray marly sands and gray calcareous muds.

The lowest occurrence (LO) of Emiliania huxleyi (0.29 Ma; base of Zone NN21) was observed between Samples 317-U1354A-6H-4, 0 cm, and 6H-CC (20.80–24.25 m) and between 317-U1354B-7H-CC and 8H-CC (26.50–33.45 m). The discrepancy in the location of this datum between Holes U1354A and U1354B is most likely due to the rare nature of this species at its inception and the paucity of nannofossils in the fine sands in Samples 317-U1354A-6H-CC and 7H-CC (24.25–31.33 m).

The highest occurrence (HO) of zonal marker Pseudoemiliania lacunosa (0.44 Ma; top of Zone NN19) was identified between Samples 317-U1354A-12H-1, 6 cm, and 12H-6, 31 cm (56.36–64.11 m), and between 317-U1354B-11H-CC and 12H-CC (57.73–62.44 m).

An intra-Pleistocene hiatus was noted between Samples 317-U1354A-15H-CC and 17H-CC (76.20–80.16 m). In Hole U1354B, this hiatus was identified between Samples 317-U1354B-15H-1, 15 cm, and 15H-1, 39 cm (73.65–73.89 m). In Hole U1354C, it was observed between Samples 317-U1354C-2H-CC and 4X-CC (72.57–84.37 m). This was evidenced by the occurrence of Gephyrocapsa >5.5 µm (1.26 Ma) at this level and the absence of Reticulofenestra asanoi (0.91–1.14 Ma), suggesting a hiatus of ~0.3 m.y. This hiatus was similarly observed at Sites U1351 and U1353, representing a robust surface of correlation between these sites. In addition, the first paleomagnetically reversed sediments were observed at 69.90 and 64.75 m (Holes U1354A and U1354B, respectively), interpreted to represent the Brunhes/Matuyama boundary (see "Paleomagnetism"). This boundary is likely unconformable, although the amount of time missing is unknown.

The HO of Helicosphaera sellii (1.34 Ma) was distinguished between Samples 317-U1354A-18H-CC and 19H-CC (80.33–85.38 m) and 317-U1354C-4X-CC and 5X-CC (84.37–86.84 m). The LO of Gephyrocapsa >4 µm (1.69 Ma) was recognized between Samples 317-U1354C-6X-CC and 7X-CC (97.76–105.86 m). Lastly, the LO of Gephyrocapsa caribbeanica (1.73 Ma) was observed between Samples 317-U1354C-8X-CC and 9X-CC (111.56–122.20 m).

Pliocene

The Pliocene/Pleistocene boundary was biostratigraphically picked using calcareous nannofossils between Samples 317-U1354C-9X-CC and 10X-CC (122.20–133.37 m). This pick correlates with a sharp lithologic boundary noted in Core 317-U1354C-10X. Site U1354 is the only expedition shelf site where this boundary was definitely recovered. Nannofossil abundances dropped dramatically across the Pliocene/Pleistocene boundary, a trend that was similarly observed at all three shelf sites. Sample 317-U1354B-12H-CC (152.98 m) contained specimens of Reticulofenestra ampla, the HO of which was dated at 2.78 Ma (Kameo and Bralower, 2000), suggesting an unconformable Pliocene/Pleistocene boundary where the late Pliocene is missing.

Nannofossil abundances in the Pliocene section were variable and ranged from barren to common, and preservation was generally good. Biostratigraphic analysis of Site U1354 Pliocene sediments was particularly problematic for all microfossil groups because of low abundances and/or the absence of biostratigraphic markers.

The HO of Reticulofenestra pseudoumbilicus (3.70 Ma) occurred between Samples 317-U1354C-16X-CC and 17X-CC (183.20–192.75 m), defining the boundary between the middle and early Pliocene. An expanded early Pliocene section was recovered from Hole U1354C, and the lowermost core catcher contained specimens of the planktonic foraminifer Globoconella puncticuloides s.s., restricting the age to younger than 4.3 Ma. Bottom-hole age was therefore constrained between 3.7 and 4.3 Ma.

Planktonic foraminifers

Holocene to late early Pliocene planktonic foraminiferal biostratigraphy of outer shelf Site U1354 was based on the examination of core catcher samples from Holes U1354A–U1354C (Tables T6, T7, T8, T9, T10, T11). Absolute ages assigned to biostratigraphic datums follow the references listed in Table T3 in the "Methods" chapter. Planktonic foraminifers were present in most samples in the Holocene to Pleistocene succession, but abundances were generally low. Preservation was generally good. For planktonic foraminiferal abundance and interpretation of oceanicity, see Tables T6, T7, and T8 and Figure F14.

Holocene

Mudline samples (317-U1354A-1H-1, 0 cm [0.00 m], and 317-U1354B-1H-1, 0 cm [0.00 m]) were characterized by abundant planktonic foraminiferal assemblages with common temperate taxa interpreted to have been deposited under extraneritic conditions. Although not identified biostratigraphically, the base of the Holocene was tentatively located at Section 317-U1354A-2H-1, 25 cm (4.03 m), at the level of distinct lithologic change between greenish gray marly sands and gray calcareous muds.

Pleistocene

Planktonic foraminiferal assemblages in the Pleistocene sections of Samples 317-U1354A-1H-CC through 19H-CC (3.78–85.38 m), 317-U1354B-1H-CC through 15H-CC (4.06–77.25 m), and 317-U1354C-2H-CC through 10X-CC (72.57–133.37 m) were characterized by small, thin-walled neritic forms. Deposition generally occurred under sheltered inner neritic conditions, except in Samples 317-U1354A-5H-CC (14.69 m), 8H-CC through 11H-CC (38.14–60.14 m), and 317-U1354B-7H-CC through 12H-CC (26.50–62.44 m), where planktonic abundances ranged from 10% to 51%, indicating deposition under inner neritic to extraneritic conditions. Peaks in abundance were generally associated with greenish gray sandy marls, and the assemblages included common temperate forms such as Globoconella inflata, Neogloboquadrina incompta, and Orbulina universa. Intervals of gray calcareous muds interbedded with sandy marls contained colder water assemblages, although the abundance of the subantarctic species Neogloboquadrina pachyderma was seldom high. Other species found in Pleistocene samples included abundant Globigerina bulloides, Globigerina spp., Turborotalita quinqueloba and related forms, and rare Globigerinita glutinata. Single specimens of the subtropical species Globigerinoides ruber (Sample 317-U1354B-12H-CC [62.44 m]) and Globigerinella aequilateralis (Sample 317-U1354A-11H-CC [60.14 m]) were also present.

Planktonic foraminifers were too few for reliable dating, but the presence of Truncorotalia truncatulinoides in Samples 317-U1354A-8H-CC (38.14 m) and 10H-CC (53.76 m) indicated that the uppermost part of the section was younger than 1.1 Ma. The late Pleistocene, Haweran/Castlecliffian Stage boundary was identified between Samples 317-U1354B-9H-CC and 10H-CC (41.46–50.29 m) on the basis of the HO of benthic foraminifer Siphotextularia wairoana. Calcareous nannofossil dating supported this correlation. The base of the Pleistocene was identified using calcareous nannofossil evidence between Samples 317-U1354C-9X-CC and 10X-CC (122.20–133.37 m).

Pliocene

Pliocene planktonic foraminiferal abundances between Samples 317-U1354C-11X-CC and 36X-CC (144.95–375.33 m) seldom reached >5% of the total foraminiferal assemblage. Assemblages were generally composed of small, thin-walled neritic forms, and diversity was low, except in Sample 317-U1354C-21X-CC (240.77 m), where planktonic abundance reached 21%. This sample included abundant small Globigerina spp., Globigerina bulloides, Neogloboquadrina pachyderma, and Nq. incompta. These species were also present in most of the Pliocene section along with sporadic occurrences of Turborotalita quinqueloba.

Several age-diagnostic species were also found in the lower part of the Pliocene section, including Globoconella inflata and Gc. puncticuloides. The HO of Zeaglobigerina woodi (2.7 Ma) was noted between Samples 317-U1354C-27X-CC and 28X-CC (293.32–299.64 m), although calcareous nannofossil dating suggested that this bioevent was suppressed at this site. The joint occurrence of Zg. woodi and Gc. puncticuloides in the lowermost Sample 317-U1354C-36X-CC (375.33 m) indicated a late early Pliocene age of 2.7–4.3 Ma for the hole bottom. Calcareous nannofossils indicated that bottommost sediments were older than 3.7 Ma, constraining the bottom-hole age to 3.7–4.3 Ma.

Benthic foraminifers

Sixty-five core catcher samples from Holes U1354A–U1354C were examined for benthic foraminifers (Table T12). Three samples identified by nannofossil biostratigraphy as caved (Table T5) were not used for biostratigraphic and paleowater depth assessments. Benthic foraminifer abundance varied throughout the cored interval. Preservation was generally good (but occasionally moderate or poor) in the Pleistocene and varied from poor to good in the Pliocene. Three benthic foraminiferal bioevents were identified at Site U1354 (Table T4).

Holocene–Pliocene

The HO of Siphotextularia wairoana (0.34 Ma) was observed between Samples 317-U1354A-9H-CC and 10H-CC (46.88–53.76 m) and between 317-U1354B-9H-CC and 10H-CC (41.46–50.29 m). Proxifrons advena (HO = ~0.4 Ma; Hayward, 2001) was also identified between Samples 317-U1354A-9H-CC and 10H-CC (46.88–53.76 m). The HO of Bolivinita pliozea (~0.6 Ma) was identified between Samples 317-U1354A-12H-CC and 13H-CC (64.90–73.44 m) and between 317-U1354B-10H-CC and 11H-CC (50.29–57.73 m). This species was also observed in the uppermost core catcher sample in Hole U1354C (2H-CC [72.57 m]), suggesting an age older than 0.6 Ma. These ages are in general agreement with Pleistocene ages derived from calcareous nannofossils. The HO of Haueslerella parri (1.63 Ma) was seen in Sample 317-U1354C-12X-CC (152.98 m) below the Pliocene/Pleistocene boundary.

Paleowater depths

Estimated paleowater depths are given in Table T12 and Figure F15. The paleodepth zone classification is given in Figure F7 in the "Methods" chapter.

In the Pleistocene section, two alternating benthic foraminiferal assemblages were noted (Holes U1354A and U1354B and Samples 317-U1354C-1H-1, 0 cm, through 9X-CC [0–122.20 m]). One assemblage consisted mainly of Notorotalia inornata (shallow inner shelf) and Elphidium charlottense (estuarine–subtidal) associated with Zeaflorilus parri (shallow inner shelf), suggesting a shallow inner shelf environment. The other assemblage consisted of Notorotalia aucklandica (inner shelf), Nonionella flemingi, and Anomalinoides sphericus (middle outer shelf), implying a depositional environment as deep as outer shelf. Samples 317-U1354A-8H-CC through 11H-CC (38.14–60.14 m) and 317-U1354C-8X-CC (111.56 m) contained the uppermost bathyal taxon Globocassidulina subglobosa. Paleowater depths exhibited high variability from subtidal to outer shelf environments, with maximum water depths in the late and earliest Pleistocene.

In the middle Pliocene section between Samples 317-U1354C-10X-CC and 22X-CC (133.37–247.41 m), benthic foraminifers were rare and poorly preserved. Notorotalia flemingi, N. aucklandica, and N. inornata (inner to middle shelf) were relatively common in association with Bolivina spp. and Astrononion spp., suggesting inner shelf environments.

In the lower Pliocene section between Samples 317-U1354C-21X-CC and 36X-CC (240.77–375.33 m), the benthic assemblage was characterized by Notorotalia flemingi, N. aucklandica, N. inornata, and Astrononion spp. (inner to middle shelf), together with consistent occurrences of Uvigerina rodleyi (inner to middle shelf; Hornibrook et al., 1989) and Anomalinoides sphericus (middle to outer shelf). This suggested middle shelf environments that shallow occasionally to inner shelf the early Pliocene.

Diatoms

Eighteen core catcher samples from Hole U1354A were examined for diatoms (Samples 317-U1354A-1H-CC through 19H-CC [3.78–85.38 m]) (Table T13). Diatom samples were typically barren, except in Sample 317-U1354A-2H-CC (12.26 m), where diatoms were common and moderately preserved. This assemblage consisted of extant coastal taxa, along with Paralia sulcata (>90% in abundance), resting spores of Chaetoceros, a fragment of Triceratium spp., and Paralia sulcata. Rare resting spores were also present in Samples 317-U1354A-4H-CC (14.30 m), 9H-CC (46.88 m), and 14H-CC (75.41 m).

All core catcher samples (317-U1354B-1H-CC through 15H-CC [4.06–77.25 m] and 317-U1354C-2H-CC through 36X-CC [72.57–375.33 m]) were barren of diatoms, except for Sample 317-U1354B-10H-CC (50.29 m), which contained two valves of the coastal species Paralia sulcata, as well as several fragments from other indeterminate species (Table T13).

Macrofossils

Macrofossils were examined in cored sediments from all Site U1354 holes. Provisional identifications, ages, and habitat preferences are provided in Table T14.

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