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doi:10.2204/iodp.proc.320321.106.2010

Biostratigraphy

At Site U1334, we recovered a 285 m thick succession of middle Miocene to uppermost middle Eocene nannofossil ooze and radiolarian clays with nannofossils. The uppermost 12 m of brown clay is barren of calcareous microfossils but contains radiolarians of middle Miocene age. Nannofossil ooze and radiolarian clays occur in the Miocene and Eocene parts of the section, with nannofossil ooze dominant in the thick Oligocene sequence. Radiolarians are present through most of the section, apart from the lowermost cores, and are well preserved in the Eocene. They provide a coherent high-resolution biochronology, and there appears to be a complete sequence of radiolarian zones from Zones RN7 (middle Miocene) to RP17 (uppermost middle Eocene). Calcareous nannofossils are present and moderately to well preserved through most of the succession, and there appears to be a complete sequence of nannofossil zones from Zone NN6 (middle Miocene) to upper Zone NP17 (uppermost middle Eocene). Nannofossil zonal determinations agree well with the radiolarian biostratigraphy; an integrated calcareous and siliceous microfossil biozonation is shown in Figure F13. A detailed age-depth plot including biostratigraphic and paleomagnetic datums is shown in Figure F14. Planktonic foraminifers are present through most of the succession and are relatively abundant and well preserved from the lower Miocene to the lower Oligocene. The preservation and abundance of planktonic foraminifers is more variable in the middle Miocene and upper Eocene to lowermost Oligocene. Benthic foraminifers are present through most of the section and indicate lower bathyal to abyssal paleodepths.

Calcareous nannofossils

Calcareous nannofossil biostratigraphy is based on analysis of core catcher samples from all three holes and from samples from most core sections of Hole U1334A. Depth positions and age estimates of biostratigraphic marker events are shown in Table T3. Nannofossils are generally abundant and moderately to well preserved throughout. Distinct intervals of poor nannofossil preservation are associated with dark lithologies within light–dark cycles around the early/middle Miocene boundary (Cores 320-U1334A-4H through 6H) and the Oligocene/Miocene boundary (Cores 320-U1334A-9H through 12H). Nannofossils are also less abundant and less well preserved in the low carbonate interval immediately below the Eocene/Oligocene boundary (Cores 320-U1334A-27H and 28H).

The uppermost interval of the succession, from Samples 320-U1334A-1H-1, 100 cm, to 2H-3, 70 cm, is barren of nannofossils. The first moderately well preserved nannofossil assemblages, between Samples 320-U1334A-2H-6, 120 cm, and 3H-4, 50 cm, are assigned to the mid to lower part of Neogene Zone NN6 (middle Miocene) based on the presence of Coronocyclus nitescens and Calcidiscus premacintyrei and the absence of Sphenolithus heteromorphus. The top common occurrence of Cyclicargolithus floridanus (lowermost Zone NN6) is recognized in Sample 320-U1334A-3H-3, 50 cm, followed by the top of S. heteromorphus (top of Zone NN5) in Sample 320-U1334A-3H-5, 50 cm, which suggests continuous deposition through this interval. Nannofossil Zones NN4 and NN5 cannot be differentiated in this succession because of the absence of the zonal marker Helicosphaera ampliaperta; however, the presence of Discoaster petaliformis between Samples 320-U1334A-3H-5, 50 cm, and 3H-CC indicates an age of upper Zone NN4 to NN5 (Young, 1999; Raffi et al., 2006). The base of D. petaliformis has been calibrated at 15.70 Ma at ODP Sites 925 and 926 (Discoaster signus in Raffi et al., 2006) and at this site occurs in Sample 320-U1334A-3H-CC. This is followed by the intra–Zone NN4 datum top common Discoaster deflandrei in Sample 320-U1334A-4H-2, 70 cm.

Calcareous nannofossils are generally poor to moderately well preserved within Cores 320-U1334A-4H and 5H, and because of the absence of Sphenolithus belemnos, probably due to poor preservation, the base of Zone NN4 cannot be distinguished. Nannofossil preservation improves and abundance increases just below the top of Triquetrorhabdulus carinatus in Sample 320-U1334A-5H-4, 120 cm, which marks the base of Zone NN3. The base of Discoaster druggii occurs in Sample 320-U1334A-9H-CC, marking the base of Zone NN2, but this species is only sporadically distributed in Cores 320-U1334A-5H through 9H. Supplementary biostratigraphic events in this Zone NN1–NN2 interval are the top of the T. carinatus acme event (Raffi et al., 2006) in Sample 320-U1334A-9H-CC, the base of Sphenolithus disbelemnos in Sample 320-U1334A-8H-CC, and the top and base of S. delphix, which are present in Samples 320-U1334A-10H-CC and 11H-1, 20 cm, respectively. The top of S. delphix occurs just prior to the Oligocene/Miocene boundary.

The Oligocene succession is dominated by white nannofossil oozes with abundant nannofossils that are moderately to well preserved. Initial nannofossil biostratigraphy indicates that this is a complete Oligocene sequence with consistently high sedimentation rates (~15 m/m.y.). The top of Zone NP25 is recognized by the top of Sphenolithus ciperoensis in Sample 320-U1334A-12H-CC. The intra–Zone NP24 abundance crossover from Triquetrorhabdulus longus to T. carinatus occurs between Samples 320-U1334A-12H-CC and 12H-7, 30 cm, and the top of Cyclicargolithus abisectus in Sample 320-U1334A-13H-1, 45 cm. The presence of all three sphenolith species, S. ciperoensis, Sphenolithus distentus, and Sphenolithus predistentus, in Sample 320-U1334A-16H-CC indicates Zone NP24 age and is also the base of consistent and common S. ciperoensis and the top of S. distentus and S. predistentus. Zones NP24–NP21 are recognized using the base of S. ciperoensis in Sample 320-U1334A-18H-CC; the top of Reticulofenestra umbilicus in Sample 320-U1334A-25X-1, 80 cm; and the top of Coccolithus formosus in Sample 320-U1334A-26X-3, 100 cm. The base of S. distentus is an intra–Zone NP23 datum and occurs in Sample 320-U1334A-21H-CC.

The age-depth plot for Site U1334 (Fig. F14) suggests that there is a calibration problem with the S. ciperoensis datums. The base of S. ciperoensis is difficult to locate because of rare and sporadic occurrences through its lower range followed by a distinct but short abundance peak near the tops of S. distentus and S. predistentus. The calibration of 27.1 Ma (Blaj et al., 2009) appears to be coincident with the base of the abundance peak and not its full range, which appears to be ~1 m.y. older and closer to the calibration used during Leg 199 (28.1 Ma) (Lyle, Wilson, Janecek, et al., 2002; see discussion in Wei and Wise, 1989).

The Eocene/Oligocene boundary interval lies between the top of C. formosus and the top of Discoaster saipanensis, which occurs in Sample 320-U1334A-27X-CC. The boundary interval yields nannofossils throughout and is apparently complete at the resolution provided by the nannofossil biostratigraphy. Eocene nannofossil Zones NP19–NP20 through NP17 are recognized using the base of Isthmolithus recurvus in Sample 320-U1334A-29X-CC, base of C. oamaruensis in Sample 320-U1334A-30X-1, 66 cm, and top of C. grandis in Sample 320-U1334A-30X-2, 74 cm. Both I. recurvus and C. oamaruensis are mid- to high-latitude taxa (Wei and Wise, 1989) and are present only rarely and sporadically at Site U1334. The presence of Dictyococcites bisectus to the base of the section indicates that the oldest sediment is between 37.1 and 38.0 Ma (upper Zone NP17).

Radiolarians

The radiolarian stratigraphy at Site U1334 (Fig. F14; Table T4) spans the interval from Zone RN7 (upper Miocene) in the base of Core 320-U1334-1H to the uppermost part of Zone RP17 (middle Eocene) in Sample 320-U1334-30X-2, 120–122 cm (Tables T5, T6, T7). The upper part of the first core (Samples 320-U1334A-1H-2, 105–107 cm, and 1H-4, 105–107 cm) recovered poorly preserved, reworked older radiolarians of Oligocene through early Miocene age. No reliable age determination could be made for these samples; however, the youngest species identified was Calocycletta costata (last occurrence at 14.23 Ma). In the Miocene through Oligocene interval, the radiolarian assemblage contains traces of reworked older microfossils, particularly in the upper Oligocene sediments (Zone RP21; Cores 320-U1334-10H, 11H, and 16H through 21H). Reworked older radiolarians are also found in the uppermost Eocene interval (Zone RP19; Cores 320-U1334A-27X and 28X). Radiolarians are usually moderately well preserved, but intervals of poor preservation are found in the uppermost part of the section (Zones RP5–RP7; Cores 320-U1334A-1H through 3H), as well as in parts of the upper Oligocene (Zone RP21; Cores 320-U1334A-17H through 20H). As in all other sites, the lowermost Oligocene (lower part of Zone RP20; Cores 320-U1334A-23X through 26X) contain common to abundant diatom frustules in the >63 µm, acid-treated fraction.

The Eocene section is indurated and the contained radiolarians are encrusted with clay and reprecipitated silica. Cleaning with a strong base solution (45% KOH) removed most of the encrustation and allowed the reliable identification of species, even for samples in which the microfossils were fragmented and poorly preserved (Samples 320-U1334A-27X-CC, 28X-2, 126–127 cm, 28X-CC, 29X-2, 50–52 cm, and 30X-2, 120–122 cm). Below Sample 320-U1334A-30X-2, 120–122 cm, sediments are barren of radiolarians.

Diatoms

Diatoms were examined in core catcher samples, as well as other samples obtained from Holes U1334A and U1334B. The interval examined represents the Craspedodiscus coscinodiscus Zone and the Rossiella fennerae through Coscinodiscus excavatus Zones of Barron (1985, 2006) and Barron et al. (2004). Diatoms range in abundance from rare to abundant depending on the specific sample. Diatom preservation is variable but generally moderate. Diatoms are typically absent or are rare in the core catcher samples from the upper eight cores. The exceptions are Samples 320-U1334A-1H-CC and 320-U1334B-1H-CC, which contain a middle Miocene diatom assemblage consisting of Cavitatus jouseanus, Rossiella paleacea, Thalassiosira yabei, C. coscinodiscus, and Denticulopsis simonsenii. Several of these species are suggestive of placement in the lower portion of the C. coscinodiscus Zone. Note that reworking of older specimens, such as Rocella vigilans, is recognized in this sample. No zonal assignment is possible for Samples 320-U1334A-2H-CC through 8H-CC.

The interval from Samples 320-U1334A-9H-2, 110–111 cm, through 10H-4, 110–111 cm, is assigned to the R. fennerae Zone based on the occurrence of Bogorovia veniamini and Craspedodiscus barronii without Rocella gelida or R. vigilans. Also characteristic of this interval are C. jouseanus, Azpeitia oligocenica, R. paleacea, and Cestodiscus pulchellus.

The interval from Samples 320-U1334A-10H-CC through 13H-2, 115–116 cm, is assigned to the R. gelida Zone based on the occurrence of R. gelida and C. baronii in this interval. This zonal assignment is supported by the occurrence of Rocella schraderi in Sample 320-U1334A-12H-2, 115–116 cm.

Diatoms are rare and typically have poor preservation in the interval from Samples 320-U1334A-13H-CC through 16H-2, 110–111 cm. The zonal assignment for this interval is tentative. Rozellea vigilans occurs in most samples examined in this interval. The occurrence of B. veniamini in Section 320-U1334A-15H-2 and Sample 320-U1334A-15H-4, 110–111 cm, suggests placement of these samples in the B. veniamini Zone. Such a zonal placement is supported by the occurrence of Cestodiscus kugleri in Sample 320-U1334A-14H-2, 110–111 cm.

The interval from Samples 320-U1334A-16H-4, 110–111 cm, through 20H-2, 115–116 cm, is assigned to the R. vigilans Zone based on the occurrence of R. vigilans without B. veniamini. The occurrence of Kozloviella minor in Sample 320-U1334A-17H-2, 110–111 cm, suggests placement of this sample in Subzone C of the R. vigilans Zone. The occurrence of Rossiella symmetrica in Sample 320-U1334A-17H-4, 110–111 cm, suggests placement of this sample in Subzone B of the R. vigilans Zone. Samples examined immediately below this interval (Samples 320-U1334A-20H-4, 115–116 cm, through 22H-CC) contain rare diatoms or poor preservation and are not zoned.

Section 320-U1334A-23X-2 is assigned to the Cestodiscus trochus Zone based on the occurrence of C. trochus without R. vigilans or C. excavatus. The interval from Samples 320-U1334A-23X-4, 90–91 cm, through 26X-4, 111–112 cm, is assigned to the C. excavatus Zone based on the occurrence of C. excavatus. Samples examined in Cores 320-U1334A-27X and below are unzoned because of the paucity of diatoms and/or the state of diatom preservation. One sample of note in this interval is Sample 320-U1334A-29X-1, 129–130 cm, which contains common diatom fragments including Hemiaulus.

Planktonic foraminifers

Core catchers were sampled from all three holes at Site U1334, and additional samples were taken in Hole U1334A (two per core) to develop a high-resolution biostratigraphy. Preservation and abundance is variable in the middle Miocene but improves downcore with good preservation recorded in the early Miocene and for much of the Oligocene. As found at previous Sites U1331–U1333, both preservation and abundance decreases across the Eocene/Oligocene boundary. Planktonic foraminifer biostratigraphy at this site indicates a middle Eocene through middle Miocene from Zone E13 or higher to Zone M9b/N12, which agrees well with calcareous nannofossil and radiolarian zonal determinations (Fig. F13). Depth positions and age estimates of biostratigraphic marker events identified are shown in Table T8. Taxon abundance and planktonic foraminifer preservation are shown in Table T9.

The topmost planktonic foraminifer zone recognized is Zone M9b/N12 in the middle Miocene defined by the base of Globorotalia (Fohsella) fohsi robusta in Sample 320-U1334A-2H-CC (18.11 m CSF). This sample is well preserved and contains a diverse fauna including Globorotalia (Fohsella) fohsi lobata, Sphaeroidinellopsis disjuncta, Dentoglobigerina altispira, and Paragloborotalia mayeri. Zones M5–M9a/N8–N12 are undifferentiated between Samples 320-U1334A-2H-CC and 4H-2, 38–40 cm (29.08 m CSF). Praeorbulina sicana was identified in Sample 320-U1334A-4H-2, 38–40 cm, but the base of Zone M5 was undefined because underlying Samples 320-U1334A-4H-CC, 320-U1334B-4H-CC, and 320-U1334C-4H-CC are barren or contain only very rare planktonic foraminifers. Zones M2–M4 were determined between the last occurrences of P. kugleri and P. pseudokugleri and the barren interval above which Zone M5 is identified. P. sicana was not found, indicating sediments younger than Zone M5. The absence of Globigerinatella insueta prevented further subdivision of Zones M2–M3, and Zones M3 and M4 were not differentiated because the last occurrence of Catapsydrax dissimilis was not reliable. The overlapping ranges of Globoquadrina dehiscens, P. kugleri, and P. pseudokugleri defines Zone M1b between Samples 320-U1334A-5H-6, 39–41 cm (44.59 m CSF), and 8H-CC (75.06 m CSF). Zone M1a occurs between the base of G. dehiscens in Sample 320-U1334A-8H-CC (75.06 m CSF) and the base of P. kugleri in Sample 320-U1334A-10H-2, 38–40 cm (86.08 m CSF).

The Oligocene/Miocene boundary is constrained at Site U1334 between Samples 320-U1334A-10H-2, 38–40 cm (86.08 m CSF), and 10H-5, 38–40 cm (90.58 m CSF), by the base of P. kugleri, which is present throughout its stratigraphic range in low abundance. Zone O6 is determined between the base of P. kugleri and the top of Paragloborotalia opima. The top and base of P. opima between Samples 320-U1334A-17X-2, 10–12 cm (152.58 m CSF), and 22X-4, 38–40 cm (203.80 m CSF), respectively, indicates Zones O2–O5. The lowest occurrence or base of Globigerina angulisuturalis falls within the range of P. opima in Sample 320-U1334A-19X-2, 38–40 cm (172.18 m CSF), and enables the distinction of Zones O4 and O5. The paucity of Chiloguembelina cubensis prevents Zones O4 and O5 from being differentiated. The top of Turborotalia ampliapertura is defined in both Holes U1334B and U1334C between Samples 320-U1334B-22H-CC and 23X-CC and Samples 320-U1334C-22H-CC and 23X-CC, respectively (Table T8). At Site U1334A, T. ampliapertura occurs sporadically and the datum is found at a lower stratigraphic level. It is not possible to divide planktonic foraminifer Zones O1 and O2 because of the absence of Pseudohastigerina naguewichensis from the assemblage.

As noted at previous sites, definition of the Eocene/Oligocene boundary is hindered by the absence of Hantkenina, which may at least in part be attributed to enhanced dissolution during this time interval and, thus, reduced foraminifer abundances and preservation but also related to the paleoecological preferences of the late Eocene hantkeninids (Coxall et al., 2003). In the absence of Hantkenina sp., the Eocene/Oligocene boundary is approximated at Site U1334 using the first occurrence of Globoquadrina venezuelana in Sample 320-U1334C-25X-CC (233.32 m CSF) and the first consistent presence of Catapsydrax unicavus in Sample 320-U1334C-26X-CC (240.51 m CSF). This approximation agrees well with the placement of the Eocene/Oligocene boundary in Tanzania (Wade and Pearson, 2008) and the radiolarian and nannofossil biostratigraphy.

Middle–late Eocene sediments contain a moderately preserved assemblage indicative of Zones E13–E16. The assemblage is dominated by small parasubbotinids, paragloborotaliids, and subbotinids. Taxa identified include Dentoglobigerina tripartita, Paragloborotalia griffinoides, Parasubbotina griffinae, Paragloborotalia nana, Subbotina angiporoides, Subbotina eocaena, Turborotalia increbescens, and Turborotalia pomeroli. The lack of Globigerinatheka, Acarinina, and Morozovelloides prevents differentiation of individual zones within the middle–late Eocene. The presence of Subbotina linaperta in Sample 320-U1334A-30X-6, 48–50 cm (280.08 m CSF), indicates a basement age older than 37.7 Ma (Berggren et al., 1995). This is consistent with the age of basement estimated using calcareous nannofossils between 37.1 and 38.0 Ma.

Benthic foraminifers

Benthic foraminifers were examined semiquantitatively from the three holes of Site U1334. Benthic foraminifers are almost continuously present in samples from Site U1334. The distribution of benthic foraminifers at this site is shown in Table T10.

The uppermost sample in Hole U1334A (Sample 320-U1331A-1H-CC; 8.22 m CSF) contains only rare benthic foraminifers and preservation varies from poor to moderate. In Samples 320-U1334A-2H-CC and 3H-CC (18.14 and 27.68 m CSF, respectively), Oridorsalis umbonatus, Nuttallides umbonifer, Cibicidoides mundulus, and Globocassidulina subglobosa are common and Pullenia bulloides, Spheroidina bulloides, Melonis pomplioides, and Melonis barleeanum are subordinate. A similar fauna is found in Samples 320-U1334B-1H-CC through 3H-CC (13.71–32.65 m CSF) and 320-U1334C-1H-CC through 3H-CC (9.84–28.10 m CSF). Middle Miocene taxa identified here indicate lower bathyal and abyssal paleodepths (van Morkhoven et al., 1986).

In Samples 320-U1334A-4H-CC through 25X-CC (37.21–233.98 m CSF), O. umbonatus, N. umbonifer, C. mundulus, G. subglobosa, and Gyroidinoides spp. are common and P. bulloides, Astrononion echolsi, and Cibicidoides grimsdalei are subordinate. Samples 320-U1334A-4H-CC and 9H-CC (37.21 and 84.77 m CSF, respectively) contain rare benthic foraminifers, but agglutinated forms are common. Preservation of foraminifer tests is good to moderate, except in Samples 320-U1334A-4H-CC and 9H-CC. Similar benthic foraminifer taxa are also recognized in Holes U1334B (Samples 320-U1334B-4H-CC through 26X-CC; 41.95–247.89 m CSF) and U1334C (Samples 320-U1334C-4H-CC through 26X-CC; 38.30–240.73 m CSF). There is no marked difference in faunal composition or preservation of benthic foraminifers between the green-colored sediments (e.g., Samples U1334A-16H-CC through 20H-CC) and other white-colored sediments in the Oligocene. Faunal compositions recorded here indicate lower bathyal and abyssal paleodepths during the Oligocene and the early Miocene, similar to those of Sites U1332 and U1333 and previous studies in the eastern equatorial Pacific (ODP Site 573, Thomas, 1985; ODP Sites 1218 and 1219, Takata and Nomura, 2005). N. umbonifer and C. mundulus occur in high abundances in the Oligocene of Site U1334, but they show a more sporadic stratigraphic distribution than at Sites U1332 and U1333 (Fig. F15). Other minor species—C. grimsdalei, P. bulloides, S. bulloides, A. echolsi, and Gyroidinoides spp.—have more variable abundances than observed at Sites U1332 and U1333. These subtle differences in Oligocene benthic foraminifer fauna may arise from variations in water mass properties with depth. For example, the discontinuous abundance of N. umbonifer, a species tolerant to carbonate undersaturation and/or low food supply (e.g., Mackensen et al., 1990; Schmiedl et al., 1997), at Site U1334 in the Oligocene could be interpreted as a reduced influence of Southern Component Water and/or carbonate undersaturation of deep water compared to other sites.

Benthic foraminifers are present in Samples 320-U1334A-26X-CC through 31X-CC (243.39–283.92 m CSF), including common O. umbonatus, Nuttallides truempyi, C. grimsdalei, and G. subglobosa. Similar occurrences are also recognized in Samples 320-U1334B-27X-CC through 29X-CC (257.73–276.92 m CSF) and 320-U1334C-27X-CC through 30X-CC (248.17–277.95 m CSF). In addition, various taxa, such as Abyssamina quadrata, Abyssamina poagi, Alabamina dissonata, Anomalinoides sp. A, and Gyroidinoides spp., are subordinate in Sample 320-U1334C-30X-CC. Preservation of these calcareous foraminifers is generally poor. These faunal assemblages suggest lower bathyal to abyssal paleodepths in the middle to late Eocene. Faunal associations of these calcareous taxa in the middle to late Eocene are basically similar to those of Sites U1331–U1333 and previous preliminary studies in the eastern equatorial Pacific (Site 1218, Wilson, Lyle, and Firth, 2006).

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