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doi:10.2204/iodp.proc.342.112.2014

Biostratigraphy

Coring at Site U1411 recovered a 255 m thick sequence of Pleistocene to upper Eocene clay and nannofossil clay. Nannofossils, planktonic foraminifers, and benthic foraminifers are present through most of the succession. A short barren interval occurs between the Pleistocene and lower Miocene–Eocene sequence. Radiolarians are only present in the uppermost Pleistocene. A relatively thin Pleistocene sequence overlies a lower Miocene to mid-Oligocene succession with relatively poor carbonate microfossil preservation followed by an expanded lower Oligocene through upper Eocene succession with excellent preservation of calcareous microfossils. The Eocene–Oligocene boundary transition has sedimentation rates of up to ~3 cm/k.y.

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

An integrated calcareous and siliceous microfossil biozonation is shown in Figure F12. An age-depth plot including biostratigraphic and paleomagnetic datums is shown in Figure F19. 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 F13.

Calcareous nannofossils

Calcareous nannofossil biostratigraphy is based on analysis of core catcher and additional working section half samples in Hole U1411B. 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 U1411, the preservation of calcareous nannofossils is generally good and moderate to good in the lower Oligocene though upper Eocene and moderate or poor in the Pleistocene and lower Miocene through mid-Oligocene. The uppermost sediment in Hole U1411B contains frequent nannofossils of Pleistocene Zone NN19, indicated by the presence of Pseudoemiliania lacunosa in the uppermost Sample 342-U1411B-1H-CC (8.48 mbsf) and absence of discoasters through Sample 3H-3, 73 cm (14.13 mbsf). The interval from Sample 3H-3, 73 cm (14.13 mbsf), to 3H-5, 80 cm (17.20 mbsf), is noncalcareous and does not contain nannofossils. The interval from Sample 3H-6, 90 cm, to 6H-CC (18.80–48.95 mbsf) yields poor to moderately preserved nannofossil assemblages with few age-diagnostic taxa, but the top of Triquetrorhabdulus carinatus in Sample 3H-6, 90 cm (18.80 mbsf), and absence of Dictyococcites bisectus suggests a correlation with Zones NN2–NP25. Samples 7H-CC through 28X-CC (53.38–254.46 mbsf) are assigned to Zones NP24–NP18 based on the occurrence of standard datums listed in Table T4. The Eocene/Oligocene boundary is identified by the top Hantkenina alabamensis planktonic foraminifer datum in Sample 342-U1411B-18H-4, 110–112 cm (158.21 mbsf), just above the top of Discoaster saipanensis in Sample 19H-CC (172.38 mbsf), which marks the top of Zone NP19/NP20. The Eocene/Oligocene boundary nannofossil assemblages are well preserved and broadly comparable to those seen at Site U1406.

Minor reworking is seen in Cores 342-U1411B-23X through 27X, and a sample with significant middle Eocene (Zone NP16) reworking is present in Core 27X (Sample 27X-3, 63 cm), in the vicinity of a thick foraminifer-rich sand layer.

Radiolarians

All core catcher samples from Hole U1411B were examined for radiolarians, and only the uppermost Sample 342-U1411B-1H-CC was found to contain them. This Pleistocene assemblage is similar to that reported at Site U1409 and is assigned to Zone RN17 based on the absence of Stylatractus universus. Underlying sediment is barren of radiolarians. Sample 14H-CC contains rare spumellarian radiolarians of uncertain age.

Planktonic foraminifers

Core catchers and additional samples from working section halves were examined in Hole U1411B. Samples contain planktonic foraminifers from Pleistocene through upper Eocene. Depth positions and age estimates of identified biostratigraphic marker events are shown in Table T6. The stratigraphic distribution of planktonic foraminifers is shown in Table T7.

Sample 342-U1411B-1H-CC (0.89 mbsf) contains Globorotalia truncatulinoides and Globorotalia inflata, indicative of a Pleistocene age (Zone PT1). Samples 2H-CC through 4H-CC (10.84–29.84 mbsf) contain poorly preserved assemblages with G. inflata, Globorotalia menardii, Globigerinoides ruber, Neogloboquadrina dutertrei, and Neogloboquadrina pachyderma without G. truncatulinoides. Because the nannofossil data suggest a Miocene age, these assemblages of Pleistocene planktonic foraminifers may reflect downhole contamination.

Sample 342-U1411B-5H-CC (39.34 mbsf) appears to be of Oligocene age, as suggested by its poorly preserved, low-diversity assemblage of Catapsydrax unicavus, Catapsydrax dissimilis, Globorotaloides suteri, and Globoquadrina venezuelana. Samples 6H-CC through 10H-CC (48.945–86.585 mbsf) are assigned an early Oligocene age (Zone O3) or older, based on the presence of Subbotina angiporoides. The top of Zone O2 is identified by the top of Turborotalia ampliapertura in Sample 11H-CC (96.25 mbsf), and the top of Zone O1 is defined in Sample 14H-CC (124.425 mbsf) by the top of Pseudohastigerina naguewichiensis and Pseudohastigerina micra. The top of Zone E16, which marks the Oligocene/Eocene boundary, is found in Sample 18H-4, 110–112 cm (158.21 mbsf), based on the top of H. alabamensis. The tops of Cribrohantkenina inflata and Turborotalia cerroazulensis occur within Zone E16, in Samples 18H-CC (162.45 mbsf) and 18H-6, 110–112 cm (161.21 mbsf), respectively. Core 342-U1411B-18H contains a rather complete succession of Hantkenina specimens and well-preserved specimens of other Eocene planktonic foraminifers, compared to the same time interval at Site U1406.

The upper Eocene interval from Sample 342-U1411B-19H-CC (162.445 mbsf) to 26X-CC (235.15 mbsf) is characterized by clay-rich sediment hosting exceptionally well preserved (“glassy”) foraminifers. Reworking of middle Eocene foraminifers is common through the upper Eocene (Cores 342-U1411B-21X through 28X), although reworked specimens are readily distinguished from in situ individuals by poor to moderate preservation and brown staining of the reworked specimens. The core catcher samples of Cores 20H through 22H contain abundant lithic fragments and pebble-sized rocks, likely originating from fall-in from the top of the hole.

The top of Zone E15, defined by the top of Globigerinatheka index, occurs in Sample 342-U1411B-19H-CC (172.375 mbsf), and Zone E14, defined by the top of Globigerinatheka semiinvoluta in Sample 24X-CC (212.54 mbsf), ranges to the base of the hole (Sample 28X-CC; 254.46 mbsf).

Benthic foraminifers

Benthic foraminifers were examined semiquantitatively in core catcher samples from Hole U1411B. Additional working section half samples taken from Cores 342-U1411B-3H, 4H, and 15H through 28X 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 lower Oligocene to upper Eocene, and more abundant in the Miocene and upper Oligocene (Fig. F13; Tables T8, T9).

Preservation of benthic foraminifer tests is generally good to very good in the lower Oligocene and upper Eocene, but poor to moderate in the Miocene and upper Oligocene succession.

The Pleistocene fauna of Sample 342-U1411B-1H-CC (0.89 mbsf) is well preserved and dominated by Oridorsalis umbonatus, Quinqueloculina sp., Uvigerina peregrina, and Uvigerina senticosa. Sample 2H-CC (10.84 mbsf) is moderately preserved and dominated by Pyrulina sp. and U. peregrina (Table T8).

The poorly preserved Miocene benthic foraminifer assemblage (Sample 342-U1411B-3H-CC; 20.26 mbsf) is characterized by a high-productivity fauna with abundant Pullenia quinqueloba, Stilostomella sp., and Stilostomella paleoceanica.

Samples 342-U1411B-4H-CC through 18H-CC (29.84–162.45 mbsf) show an Oligocene fauna dominated by infaunal taxa. Abundant calcareous taxa throughout this interval include Cassidulina subglobosa, Dentalina sp., Gyroidinoides spp., and stilostomellids (Stilostomella gracillima, Stilostomella lepidula, and Stilostomella subspinosa) (Table T8). In addition to the taxa described above, single samples are characterized by the abundant occurrence of Kalamopsis?, O. umbonatus, and Uvigerina rippensis. As also observed at sites on J-Anomaly Ridge, the dominance of infaunal taxa at Site U1411 suggests high-organic export flux to the seafloor or the prevalence of suboxic seafloor conditions during the Oligocene.

The underlying upper Eocene sequence shows benthic foraminifer assemblages that suggest a normal deepwater environment only sporadically dominated by infaunal species. Fauna are mainly dominated by C. subglobosa, Cibicidoides praemundulus, Dentalina sp., Nuttallides truempyi, P. quinqueloba, S. lepidula, S. subspinosa, and, in several samples, O. umbonatus. Sample 342-U1411B-24X-CC (212.54 mbsf) is exceptional in that it contains a benthic foraminifer assemblage dominated by the infaunal taxa Plectofrondicularia lirata and Plectofrondicularia cf. kerni.

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