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doi:10.2204/iodp.proc.339.103.2013

Biostratigraphy

A continuous record of calcareous nannofossil ooze (see “Lithostratigraphy”) was recovered at Site U1385, spanning from the early Pleistocene to the Holocene (Table T7). Samples from all core catchers of Holes U1385A–U1385D and the five lowermost core catchers of Hole U1385E were prepared for analysis. Sample 339-U1385C-1H-CC was not analyzed.

Nannofossils and planktonic foraminifers were very abundant and relatively well preserved in all samples (Tables T8, T9). For planktonic foraminifers, evidence of some fragmentation was recognized in most of the samples. Benthic foraminifers were also relatively abundant and diverse in the samples (Table T10), although their percentage with respect to planktonic foraminifers is usually <5%. By contrast, ostracods were rare in most of the samples. Their percentage with respect to planktonic foraminifers is <1%. Pteropods were not observed in any of the samples from this site but were observed in mudline samples collected from each hole (top of Core 1H). Pollen and spores are generally abundant and moderately well preserved. Concentrations ranging between 1,800 and 12,000 grains/cm³ are similar to those reported previously from the Western Iberian margin (Sánchez Goñi et al., 1999, 2009). Microcharcoal particles occur abundantly.

The chronologic framework for Site U1385 is based on the identification of a series of calcareous nannofossil and planktonic foraminifer events as well as one benthic foraminifer datum (Table T7). The distribution of calcareous nannofossil events suggests a continuous Pleistocene record at Site U1385. The calibrated biohorizons allow us to estimate a nearly uniform sedimentation rate of ~10 cm/k.y. (Fig. F16).

Calcareous nannofossils

All core catcher samples from Holes U1385A, U1385B, and U1385D were examined for calcareous nannofossil biostratigraphy. Additionally, selected samples from Hole U1385A were analyzed in order to constrain biohorizons, paying attention only to marker species. Calcareous nannofossil assemblages are abundant and diverse, and preservation is good, with weak dissolution in some samples. Small placolith species (<3 µm) dominate most of the assemblages. Inorganic input and reworking of pre-Pleistocene (mainly Neogene) species vary from few to common throughout all samples (Table T8).

In total, seven Pleistocene nannofossil datums defined and/or calibrated by Raffi et al. (2006 and references therein) and Flores et al. (2010) were identified in all Site U1385 holes (Table T7).

The change in abundance of the large Emiliania huxleyi (>4 µm) that characterizes Termination 1 in mid- to low-latitude water masses in the Atlantic Ocean has been recognized as a useful event by Flores et al. (2010). This change in abundance was recorded between Samples 339-U1385A-2H-1, 90 cm, and 2H-2, 7 cm (2.40–3.07 mbsf); between the top of the hole and Sample 339-U1385B-1H-CC (0–6.99 mbsf); and between the top of the hole and Sample 339-U1385D-1H-CC (top of the hole to 6.99 mbsf), making it possible to distinguish the onset of the Holocene in all three holes.

The first occurrence (FO) of E. huxleyi (0.26 Ma), which marks the base of Zone NN21, is ubiquitously present between Samples 339-U1385A-4H-4, 90 cm, and 4H-5, 5 cm (25.90–26.55 mbsf); between 339-U1385B-3H-CC and 4H-CC (25.44–35.12); and between 339-U1385D-3H-CC and 4H-CC (26.28–36.04 mbsf).

The last occurrence (LO) of Pseudoemiliania lacunosa (0.46 Ma), considered a globally synchronous event that defines the top of Zone NN19, occurs between Samples 339-U1385A-6H-CC and 7H-1, 40 cm (49.40–49.48 mbsf); 339-U1385B-6H-CC and 7H-CC (53.85–63.65 mbsf); and 339-U1385D-6H-CC and 7H-CC (51.92–61.42 mbsf).

A biohorizon considered useful in Pleistocene sediments is the LO of Reticulofenestra asanoi (0.90 Ma). This event was identified between Samples 339-U1385A-11H-6, 90 cm, and 11H-7, 5 cm (95.40–96.05 mbsf); 339-U1385B-10H-CC and 11H-CC (92.07–101.74 mbsf); and 339-U1385D-10H-CC and 11H-CC (89.87–99.29 mbsf). The FO of R. asanoi (1.07 Ma), another significant event for the Pleistocene, was identified between Samples 339-U1385A-13H-7, 50 cm; and 13H-CC (115.70–116.32); 339-U1385B-12H-CC and 13H-CC (110.19–120.57 mbsf); and 339-U1385D-13H-CC and 14H-CC (118.76–127.80). To define these biohorizons, specimens of R. asanoi ≥6 µm in size were considered.

The LO of large Gephyrocapsa spp. (>5.5 µm; 1.24 Ma) was recorded between Samples 339-U1385A-15H-4, 8 cm, and 15H-4, 105 cm (128.99–129.96 mbsf); 339-U1385B-13H-CC and 14H-CC (120.57–129.90 mbsf); and 339-U1385D-14H-CC and 15H-CC (127.80–137.09 mbsf).

The LO of Helicosphaera sellii (1.25 Ma) is considered a diachronous event (Raffi et al., 1993; Wei, 1993). Its occurrence at this site is consistent with the ages provided by Raffi et al. (2006) for the Mediterranean Sea. At Site U1385, the event is placed between Samples 339-U1385A-15H-5, 90 cm, and 15H-6, 5 cm (131.31–131.96 mbsf); 339-U1385B-13H-CC and 14H-CC (120.57–129.90 mbsf); and 339-U1385D-14H-CC and 15H-CC (127.80–137.09 mbsf).

Planktonic foraminifers

Both the 150 and 63 µm residues are clearly dominated by planktonic foraminifers, with very small proportions of fine-grained detrital grains in some samples, such as Sample 339-U1385B-1H-CC. The planktonic foraminifer assemblages observed at Site U1385 are typical of temperate waters from the North Atlantic with temporal increases in abundance of subtropical or polar to subpolar species (Table T9). Neogloboquadrina pachyderma (dextral), Globorotalia inflata, and Globigerina bulloides are the dominant species in most of the samples, although N. pachyderma (sinistral) during glacial times and Globigerinoides ruber during interglacials are also temporarily abundant. Orbulina universa and Globigerinella siphonifera are present in nearly all core catcher samples. Deep-dwelling species Globorotalia truncatulinoides and Globorotalia scitula are also present in most core catcher samples, with both species preferentially coiling dextral. Globorotalia crassaformis, when present, coils in either direction. Globorotalia hirsuta occurs only sporadically.

Two planktonic foraminifer bioevents were identified at Site U1385, the top and bottom of the paracme of N. pachyderma (sinistral) (Table T7). The top of the paracme is astronomically dated at 1.21 Ma and tuned to insolation Cycle i117 in the Mediterranean (Lourens et al., 1996a, 1996b) and has been reported in the northeast Atlantic (Raymo et al., 1989; Lourens et al., 1998; Sierro et al., 2009) near the bottom of the Cobb Mountain paleomagnetic subchron during MIS 36 (Sierro et al., 2009). This event was located in all holes between Samples 13H-CC and 14H-CC (116.12–124.67 mbsf in Hole U1385A, 120.57–129.90 mbsf in Hole U1385B, 118.76–127.80 mbsf in Hole U1385D, and 111.43–119.13 mbsf in Hole U1385E), although its location in Hole U1385D is ambiguous because of the rare presence of this species in Sample 339-U1385D-13H-CC.

The bottom paracme of N. pachyderma (sinistral) was only recorded in Holes U1385D and U1385E, where the species is relatively abundant after an interval of very rare occurrence above this level. Consequently, this bioevent must be placed between Samples 339-U1385D-15H-CC and 16H-CC (137.09–147.00 mbsf) and between 339-U1385E-16H-CC and 17H-CC (138.59–147.20 mbsf). The bioevent is astronomically dated in the Mediterranean at 1.37 Ma within insolation Cycle i131 (Lourens et al., 1996a). N. pachyderma (sinistral), which is abundant during glacial periods older than 1.37 Ma, almost disappears in the glacial stages of MIS 42, 40, and 38, as has been reported from the Vrica-Crotone composite section in Italy (Lourens et al., 1996b) and Deep Sea Drilling Project Site 607/IODP Site U1313 from the same location in the North Atlantic (Raymo et al. 1989; Sierro et al., 2009). This event was also observed at Ocean Drilling Program Site 967 and Hole 969D (Lourens et al., 1998). However, the low sampling resolution and the frequent changes in abundance of this species linked to glacial–interglacial fluctuations prevented identification of a more accurate position of these two events.

Because the bottom paracme of N. pachyderma (sinistral) is located at the bottom of Holes U1385D and U1385E, it was concluded that Site U1385 extends from the Holocene to 1.37 Ma.

In Samples 339-U1385A-16H-CC and 17H-CC (143.80–151.63 mbsf), 339-U1385B-15H-CC and 16H-CC (137.76–146.30 mbsf), 339-U1385D-15H-CC and 16H-CC (137.09–147.00 mbsf), and 339-U1385E-16H-CC and 17H-CC (138.59–147.20 mbsf), large, heavily encrusted specimens of Neogloboquadrina atlantica (dextral) are present (Table T9). An incursion of this species during the early Pleistocene was reported for the North Atlantic at IODP Site U1313 (Channell, Kanamatsu, Sato, Stein, Alvarez Zarikian, Malone, and the Expedition 303/306 Scientists, 2006). At that site, the top of the incursion was dated at ~1.4 Ma, based on a low-resolution biostratigraphy study. With a more accurate chronology, this event may be useful for Atlantic and Mediterranean correlations.

Benthic foraminifers

All core catcher samples from Hole U1385A were studied for the abundance of benthic foraminifers (Table T10). Additionally, selected core catcher samples from Holes U1385B and U1385D were evaluated for the “Stilostomella extinction” event. The revealed benthic assemblages are well preserved, with only a few specimens broken in each sample.

Assemblages from the lower portion of Hole U1385A are characterized by high abundances of stilostomellids, in particular Siphonodosaria lepidula and Myllostomella fijiensis. Together with the occurrences of Dentalina spp., Epistominella exigua, Fursenkoina complanata, Sphaeroidina bulloides, and Uvigerina peregrina, the assemblages suggest high flux of organic carbon to the seafloor and a poorly oxygenated environment (Kaiho, 1999; Kawagata et al., 2005; Murray, 2006).

Stilostomellids markedly decrease in abundance from Sample 339-U1385A-12H-CC to 10H-CC, until they finally disappear between Samples 10H-CC and 9H-CC (77.83–82.12 mbsf), marking the Stilostomella extinction (0.70–0.58 Ma) (Hayward, 2002; Kawagata et al., 2005). The datum is identified at similar depth intervals in Holes U1385B (72.68–82.12 mbsf) and U1385D (80.37–89.87 mbsf) and agrees well with the age between 0.90 and 0.46 Ma, as suggested by nannoplankton assemblages for the respective samples (Table T7; Fig. F16). Higher abundances of Cibicidoides spp. and Pyrgo spp. indicate higher bottom water oxygenation (Kaiho, 1999; Murray, 2006).

Subsequent assemblages from Samples 339-U1385A-9H-CC to 6H-CC constantly show high abundances of E. exigua and Cassidulina laevigata/teretis. Together with the regular occurrences of epifaunal (Cibicidoides spp.) and deep infaunal (Melonis spp., Globobulimina affinis, and Globocassidulina subglobosa) taxa, these assemblages indicate increased seasonality with pulses of high organic carbon flux and fluctuating bottom water oxygenation (Schnitker, 1984; Gooday, 1993; Kaiho, 1999; Gupta and Thomas, 2003; Bartoli et al., 2005).

In the uppermost portion of Hole U1385A (0–39.97 mbsf), the composition of the foraminiferal assemblages differs strongly between samples. In general, the assemblages show increased abundances of buliminid and bolivinid species with highly varying background fauna. Samples 339-U1385A-5H-CC to 3H-CC are mainly composed of hyaline species, whereas abundant occurrences of Rhizammina spp. (Sample 2H-CC) and spiroloculinid foraminifers (Sample 1H-CC) are documented for the top of the section. These assemblages indicate high organic carbon flux and poorly oxygenated bottom water (Kaiho, 1999; Murray, 2006).

In conclusion, the succession of benthic foraminiferal assemblages documents a deep-sea environment affected by considerable changes in surface water productivity, organic carbon flux, and ventilation of bottom water. The observed variability in benthic associations most likely reflects the impact of the Mid-Pleistocene Transition (MPT) on North Atlantic circulation patterns in general (Kawagata et al., 2005), as well as changes in regional upwelling intensity during glacial and interglacial periods.

Ostracods

Ostracods were studied from all core catcher samples in Holes U1385A and U1385B (Table T11), in which they occur in low numbers (from barren to 20 valves per sample) when compared to other North Atlantic sites at similar water depths (Cronin et al., 1999; Didié et al., 2000; Alvarez Zarikian et al., 2009). Preservation ranges from excellent to poor, and highest abundances (>10 valves per sample) are observed in the upper 45 m of the sedimentary record at Site U1385 (Samples 339-U1385B-1H-CC, 3H-CC, 4H-CC, and 5H-CC; 339-U1385A-11H-CC; and 339-U1385B-10H-CC, 14H-CC, and 16H-CC). Barren samples were observed between ~80 and 115 mbsf in Holes U1385A and U1385B, an interval dated to ~0.6–1.1 Ma or equivalent to the MPT (Fig. F16). More than 21 species belonging to 16 genera were identified overall. Samples with the highest abundance are dominated by Krithe spp. In the Atlantic Ocean, the deep-sea taxon Krithe is dominant in North Atlantic Deep Water (NADW) (Cronin et al., 1999; Didié and Bauch, 2000; Dingle and Lord, 1990; Yasuhara et al., 2009a, 2009b). Therefore, the high relative abundance of Krithe at Site U1385 can be attributed to the influence of NADW. Other taxa found at Site U1385 include Henryhowella asperrima and Cytheropteron spp., followed by Argilloecia acuminata, Australoecia posteroacuta, Poseidonamicus major, Cytherella robusta, and Echinocythereis echinata, all taxa with worldwide distribution and common in deep-sea Cenozoic sediments. Henryhowella has been recorded with highest relative abundances during interglacials at other North Atlantic sites (Cronin et al., 1999; Didié and Bauch, 2000; Alvarez Zarikian et al., 2009). Poseidonamicus is a characteristic genus of lower NADW (Dingle and Lord, 1990) and occurs in very low abundance in Samples 339-U1385A-3H-CC and 339-U1385B-3H-CC. Cytheropteron is typically associated with deglacial periods in North Atlantic deep-sea sediments (Cronin et al., 1999; Alvarez Zarikian et al., 2009), but its low overall abundance and sparse sampling intervals do not allow for any paleoceanographic interpretations at this time.

Palynology

Nine unevenly distributed samples were analyzed from Hole U1385A (Table T12). Preservation ranges from moderate to good except for the lowest level (Sample 339-U1385A-16H-CC), which shows strong alteration of palynomorphs and, in particular, corroded Conifers. Pinus is abundant, with concentrations >2000 grains/cm³ in almost all samples, excluding Samples 339-U1385A-3H-CC and 6H-CC (Fig. F17). Pollen assemblages are mainly composed of Pinus and trees and shrubs characterizing the Mediterranean forest (deciduous and evergreen Quercus, Olea, and Phillyrea), Ericaceae, grasslands (Taraxacum-type and Poaceae), and semidesert plants (Artemisia, Chenopodiaceae, Ephedra dystachia, and Ephedra fragilis). These assemblages are those typically found in southwestern Iberia over the last 425 k.y. (Sánchez Goñi et al., 1999, 2008, 2009; Tzedakis et al., 2009; Margari et al., 2010). Several experimental studies on the relationships between pollen content in marine sediments and vegetation of the adjacent continent (e.g., Heusser, 1985; Turon, 1984) and, in particular, experiments performed along the Iberian margin (Naughton et al., 2007) have shown that pollen assemblages from the Iberian margin reliably resemble the integrated (regional/subcontinental) vegetation occupying the adjacent landmass. Three samples (339-U1385A-6H-CC, 10H-CC, and 13H-CC) clearly reveal the dominance of open vegetation, semidesert, and grasslands in this region. From the uppermost sample (339-U1385A-1H-CC), the occurrence of a Mediterranean forest in southwestern Iberia was inferred that was assigned to the Holocene on the basis of previous studies (Lézine and Denèfle, 1997). The remaining samples are a mixture of both open vegetation and forest environments. Also, Sample 339-U1385A-11H-CC is characterized by high numbers of Stelladinium cf. reidii, a species of dinocyst living in warm waters (L. Londeix, pers. comm., 2011).

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