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doi:10.2204/iodp.proc.342.111.2014

Biostratigraphy

Coring at Site U1410 recovered a 260 m thick sequence of Pleistocene to lower Eocene nannofossil ooze and nannofossil clay, with foraminifers and radiolarians. Nannofossils, planktonic foraminifers, and benthic foraminifers are present through most of the succession. Short barren intervals occur between thin Pleistocene, upper Miocene, and lower Miocene–Oligocene sequences. Radiolarians are only present in the uppermost Pleistocene and lower Eocene. Thin Pleistocene, upper Miocene, and lower Miocene–Oligocene sequences overlie a middle Eocene through lower Eocene succession. Hiatuses or highly condensed intervals occur between the lower Pleistocene and upper Miocene (7.1 m.y. duration), upper and lower Miocene (7.4 m.y. duration), lower Miocene and upper Oligocene (5.4 m.y. duration), and lower Oligocene and middle Eocene (7.4 m.y. duration). The Oligocene is highly condensed and may also contain significant hiatuses. Sedimentation rates are 0.2 cm/k.y. through the Oligocene, 1.3–2.6 cm/k.y. through the middle Eocene, and 0.6 cm/k.y. through the lower Eocene.

Benthic foraminifers are generally rare (the “present” category) throughout the recovered succession with the exception of the Miocene to Oligocene, in which they are abundant to dominant. Benthic foraminifer preservation is good to very good through most of the recovered Eocene sequence. Moderate to poor preservation occurs in the Miocene to Oligocene and the early Eocene.

An integrated calcareous and siliceous microfossil biozonation is shown in Figure F13. An age-depth plot including biostratigraphic and paleomagnetic datums is shown in Figure F22. Datum and zonal determinations from nannofossils, planktonic foraminifers, and radiolarians are in close agreement. Microfossil and paleomagnetic datums are given in Table T3. A summary of calcareous and siliceous microfossil abundances and preservation is given in Figure F14.

Calcareous nannofossils

Calcareous nannofossil biostratigraphy is based on analysis of core catcher and additional working section-half samples in Hole U1410A. Depth positions and age estimates of biostratigraphic marker events are shown in Table T4. Calcareous nannofossil occurrence data are shown in Table T5. Note that the distribution charts are based on shipboard study only and are therefore biased toward age-diagnostic species.

At Site U1410, the preservation of calcareous nannofossils is generally good and moderate to good in the middle Eocene and moderate in the upper Miocene, lower Miocene–Oligocene, and lower Eocene. The uppermost sediment in Hole U1410A contains abundant nannofossils indicative of Pleistocene Zones NN20/NN21–NN17 indicated by the top of Pseudoemiliania lacunosa in Sample 342-U1410A-1H-CC (8.48 mbsf) and the top of Discoaster pentaradiatus in Sample 4H-3, 100 cm (31.51 mbsf). Samples 4H-3, 100 cm (31.51 mbsf), through 4H-CC (37.52 mbsf) are noncalcareous and do not contain nannofossils. The short interval from Sample 4H-CC to 5H-3, 100 cm (31.51–41.00 mbsf), is assigned to upper Miocene Zone NN9 based on the presence of Discoaster hamatus. The underlying sediment, from Sample 5H-3, 100 cm, to 5H-CC (41.00–46.45 mbsf), is noncalcareous and barren of nannofossils.

The interval from Sample 342-U1410A-5H-CC through 6H-5, 50 cm (46.45–53.00 mbsf), is assigned to lower Miocene–upper Oligocene Zones NN3–NN1 based on the top of Sphenolithus belemnos in Sample 5H-CC (46.45 mbsf), the base of Discoaster druggii in Sample 6H-3, 50 cm (50.00 mbsf), and the top of Sphenolithus ciperoensis in Sample 6H-5, 50 cm (50.00 mbsf). A short, poorly preserved interval, from Sample 6H-5, 50 cm, through 7H-3, 50 cm (50.00–59.55 mbsf), is late Oligocene in age (Zones NP24–NP25) based on the presence of Dictyococcites bisectus and S. ciperoensis.

The identification of Zone NP23 in Sample 342-U1410A-7H-7, 62 cm (64.17 mbsf), and Zone NP17 in Sample 342-U1410B-4H-CC, 6.5 cm (64.25 mbsf), indicates the presence of a hiatus of ~8 m.y., representing the upper Eocene to lower Oligocene.

Samples 342-U1410A-7H-7, 70 cm, through 28X-CC (64.25–258.69 mbsf) are assigned to middle to upper Eocene nannofossil Zones NP17–NP12 based on the top of Chiasmolithus grandis in Sample 7H-7, 70 cm (64.25 mbsf), the top and base of Chiasmolithus gigas in Samples 17X-2, 87 cm (153.37 mbsf), and 21X-2, 70 cm (190.74 mbsf), the base of Blackites inflatus in Sample 23X-6, 108 cm (216.28 mbsf), the base of Discoaster sublodoensis in Sample 24X-CC (227.06 mbsf), the top of Tribrachiatus orthostylus in Sample 26X-5, 90 cm (244.00 mbsf), and the presence of Discoaster lodoensis at the base of the section in Sample 28X-CC (258.69 mbsf).

Radiolarians

Radiolarian biostratigraphy is based on analysis of all core catcher samples from Hole U1410A. No samples from Hole U1410B or U1410C were examined. Radiolarians are present in the uppermost part of Hole U1410A (Cores 342-U1410A-1H and 2H) but are absent from the underlying Pleistocene–middle Eocene interval, from Core 3H to 22X (27.88–208.03 mbsf). Radiolarians are very abundant and well preserved in the upper part of the lower Eocene (Cores 23X through 25X; 218.4–233.2 mbsf) and common but poorly preserved in the lowermost Cores 26X through 28X (246.1–258.7 mbsf). Depth positions and age estimates of biostratigraphic marker events are shown in Table T6, and the radiolarian distribution is shown in Table T7. Note that the distribution charts are based on shipboard study only and are therefore biased toward age-diagnostic species.

Sample 342-U1410A-1H-CC (8.48 mbsf) contains a well-preserved Pleistocene–Holocene radiolarian assemblage assigned to Zone RN17 based on the absence of Stylatractus universus. Sample 2H-CC (18.4 mbsf) contains rare radiolarians of no biostratigraphic utility. Samples 3H-CC through 22X-CC (20.6–208.03 mbsf) are barren of radiolarians.

Below 208.03 mbsf, Hole U1410A contains a continuous radiolarian succession from Zone RP11 to RP8. Sample 342-U1410A-23X-CC (218.4 mbsf) is assigned to Zone RP11 based on the presence of the primary index species Dictyomitra mongolfieri and the absence of Eusyringium lagena, the primary index species for Zone RP12. The scarcity of D. mongolfieri suggests that this sample lies in lowermost Zone RP11. Sample 24X-CC (227.1 mbsf) is assigned to Zone RP10 based on the presence of Lithochytris vespertilio and the absence of D. mongolfieri. The event that defines the base of Zone RP10, the faunal crossover from Theocotyle nigriniae to Theocotyle cryptocephala, is poorly expressed in Hole U1410A. T. cryptocephala is much less common than T. nigriniae in both samples that span the Zone RP10–RP11 interval. Sample 25X-CC (233.2 mbsf) is assigned to Zone RP9 based on the presence of Lamptonium fabaeforme constrictum and the absence of Lamptonium vespertilio and T. cryptocephala. Samples 26X-CC through 28X-CC (246.1–258.7 mbsf) contain common radiolarians of poor to moderate preservation and are assigned to Zone RP8 based on the presence of the primary index, Buryella clinata. The top of Buryella tetradica is recorded at the top of the zone (Sample 26X-CC; 246.1 mbsf).

Planktonic foraminifers

Core catchers and additional samples from Hole U1410A working section halves were examined. Samples contain planktonic foraminifers from the Pleistocene through lower Eocene. Depth positions and age estimates of identified biostratigraphic marker events are shown in Table T8. The stratigraphic distribution of planktonic foraminifers is shown in Table T9.

The uppermost interval from Sample 342-U1410A-1H-CC to 2H-CC (8.48–18.36 mbsf) contains Globorotalia truncatulinoides and Globorotalia inflata, indicative of Pleistocene age. Sections 342-U1410A-3H-CC through 4H-5 (27.88–34.51 mbsf) contain a poorly preserved low-diversity assemblage dominated by G. inflata, Neogloboquadrina dutertrei, and Neogloboquadrina pachyderma, suggesting an age of late Pliocene–Pleistocene. An upper Miocene assemblage was recovered from Samples 4H-6, 100–102 cm, through 5H-3, 100–102 cm (36.01– 41.01 mbsf), with the co-occurrence of Globoturborotalita nepenthes, Globorotalia plesiotumida, and Sphaeroidinellopsis seminulina and the absence of Globorotalia tumida and Sphaeroidinella dehiscens, suggesting Subzone M13b to Zone M14.

Three barren intervals occur from Sample 342-U1410A-5H-4, 100–102 cm, to 5H-5, 100–102 cm (42.51–44.01 mbsf); from Sample 6H-6, 100–102 cm, to 6H-CC (55.01–56.20 mbsf); and in Sample 7H-7, 28–30 cm (63.84 mbsf). Samples 5H-6, 90–92 cm, to 6H-4, 100–102 cm (45.41–52.01 mbsf), contain no planktonic foraminifers or poorly preserved and impoverished assemblages of early Miocene age (Zone M3 or older) consisting of Catapsydrax dissimilis, Globorotalia praescitula, and Globigerinoides immaturus. A poorly preserved and impoverished assemblage of Oligocene age (unzoned) exists from Sample 7H-2, 100–102 cm, to 7H-5, 100–102 cm (58.53–61.9 mbsf).

Sample 342-U1410A-7H-7, 100–102 cm, contains diverse globigerinathekids, Subbotina senni, Turborotalita carcoselleensis, and Turborotalia cerroazulensis, suggesting middle Eocene Zone E13. Well-preserved and diverse planktonic foraminifers of early to middle Eocene age are found in Samples 7H-CC through 23X-5, 102–104 cm (65.66–215.53 mbsf). The top and base of Orbulinoides beckmanni demarcates the top and base of Zone E12 in Samples 8H-4, 110–112 cm, and 9H-CC (71.11–84.56 mbsf). The top of Guembelitrioides nuttalli marks the base of Zone E11 in Sample 10H-6, 90–92 cm (90.56 mbsf). Although the top of Morozovella aragonensis marks the base of Zone E10, this species occurs only sporadically through the middle Eocene of Hole U1410A. Therefore, we have used the base of Morozovella lehneri in Sample 17X-4, 120–122 cm (156.71 mbsf), to approximate this zonal boundary. The base of Globigerinatheka kugleri occurs in Sample 17X-CC (160.82 mbsf) and marks the base of Zone E9. The base of G. nuttalli in Sample 22X-2, 100–102 cm (201.51 mbsf) indicates the base of Zone E8, and the base of Turborotalia frontosa in Sample 23X-5, 102–104 cm (215.53 mbsf), marks the base of Subzone E7b.

The early Eocene interval from Sample 342-U1410A-23X-CC to 27X-CC (218.43–255.14 mbsf) contains poorly preserved planktonic foraminifers ranging from Subzone E7a through Zone E5. The base of Acarinina cuneicamerata in Sample 26X-2, 114–115 cm (239.75 mbsf), indicates the base of Subzone E7a, whereas the top of Morozovella subbotinae in Sample 27X-CC (252.83 mbsf) marks the top of Zone E5.

Benthic foraminifers

Benthic foraminifers were examined semiquantitatively in core catcher samples from Hole U1410A. Additional working section half samples taken from Cores 342-U1410A-4H through 27X were examined for preservation and relative abundance of benthic foraminifers. Benthic foraminifers at this site are predominantly rare (the “present” category) relative to total sediment particles >150 μm in the Pleistocene and Eocene, and more abundant in the Miocene and Oligocene (Fig. F14; Tables T10, T11).

Preservation of benthic foraminifer tests is generally good to very good in the middle Eocene, the Miocene, and Oligocene, but the lower Eocene successions contain poorly to moderately preserved benthic foraminifers (Fig. F14).

With the exception of well-preserved Sample 342-U1410A-1H-CC (8.48 mbsf), the Pleistocene faunas of Samples 1H-CC through 3H-CC (8.48–27.88 mbsf) are moderately preserved and dominated by Cibicidoides sp., Cibicidoides kullenbergi, Cibicidoides wuellerstorfi, Pullenia bulloides, Turrilina sp., and Uvigerina peregrina (Table T10).

The moderately preserved Miocene benthic foraminifer assemblage (Samples 342-U1410A-4H-CC and 5H-CC; 37.52–46.45 mbsf) is characterized by high-productivity fauna with abundant Cassidulina subglobosa, Dentalina sp., Gyroidinoides sp., Plectofrondicularia sp., Pleurostomella tenius, Stilostomella subspinosa, and Turrilina sp.

Poorly preserved Oligocene benthic foraminifers are found in Sample 342-U1410A-6H-CC (56.20 mbsf). This sample contains abundant glauconite grains and fish teeth, indicative of a condensed sequence with low sedimentation rate. Because of this condensed nature, benthic foraminifers, potentially exposed on the seafloor for a long interval of time, are severely fragmented and dissolved.

Samples 342-U1410A-7H-CC through 28X-CC (65.66–258.69 mbsf) show typical early to middle Eocene fauna dominated by calcareous taxa. Abundant calcareous taxa in the middle Eocene are Anomalinoides sp., Bulimina sp., Cassidulina subglobosa, Cibicidoides praemundulus, Dentalina sp., Nuttallides truempyi, Oridorsalis umbonatus, Pullenia bulloides, and stilostomellids (including Stilostomella gracillima, Stilostomella lepidula, and Stilostomella subspinosa) (Table T10). In addition to the taxa described above, the lower Eocene and lowermost middle Eocene (Samples 342-U1410A-21X-CC through 28X-CC; 199.13–258.69 mbsf) are characterized by the occurrence of Alabamina dissonata, Aragonia aragonensis, and Cibicidoides eocaenus.

The lower to middle Eocene assemblages described above suggest a normal deepwater environment, but Sample 342-U1410A-11H-CC (103.18 mbsf) is exceptional in that it contains a benthic foraminifer assemblage dominated by the infaunal taxa Bigenerina sp. and Stilostomella spp. together with abundant N. truempyi and lacks other epifaunal species. A short-term increase in infaunal taxa can be also found within the MECO-equivalent sequence (Section 342-U1410A-8H-CC; 75.39 mbsf), comparable to observations from the same level at Site U1408.

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