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doi:10.2204/iodp.proc.339.108.2013

Biostratigraphy

Sediment at Site U1390 dates from the Holocene to the mid-Pleistocene (Fig. F20; Table T6), with the base age of Hole U1390A estimated at younger than 1.4 Ma. The absence of relevant and characteristic calcareous nannofossil bioevents in the micropaleontological succession allows us to define two hiatuses covering the interval between 0.3–0.6 and 0.9–1.2 Ma. The older hiatus is, furthermore, indicated by the co-occurrence of the “Stilostomella extinction” event (0.58–0.7 Ma) and the top of the paracme of Neogloboquadrina pachyderma (sinistral) (1.21 Ma) between Samples 339-U1390A-31X-CC and 32X-CC (Table T6).

A sedimentation rate of ~75 cm/k.y. has been estimated for the upper part of the site, whereas intervals below the younger hiatus are close to 85 cm/k.y., although the absence of precise age control prevents an accurate calculation (Fig. F20).

The microfossil content of sediment recovered at Site U1390 was usually high. The samples are rich in planktonic and benthic foraminifers as well as calcareous nannofossils (Tables T7, T8, T9). Pteropod fragments were found in several samples and in Sample 339-U1390A-2H-CC, their occurrence is even common. Ostracods were not studied at Site U1390.

Pollen and spores are abundant in the seven samples analyzed in Hole U1390A, ranging from ~6,000 to 60,000 grains/cm3. These figures are similar to those found at the previous sites in the Gulf of Cádiz. However, they are 10 to 50 times lower than the values observed in Holocene sediment from the Guadiana estuary (Fletcher et al., 2007), located 100 km north on the Portuguese coast. The preservation of the grains is mostly good to moderate. The proportion of unidentifiable grains progressively increases toward the bottom of the sequence, as is the case at Sites U1387 and U1389 (Fig. F26 in the “Site U1387” chapter [Expedition 339 Scientists, 2013e] and Fig. F22 in the “Site U1389” chapter [Expedition 339 Scientists, 2013g]). Microcharcoal particles and dinocysts were also observed.

Calcareous nannofossils

We examined all core catcher samples from Holes U1390A–U1390C for calcareous nannofossil biostratigraphy. The assemblages are abundant to very abundant. The preservation is good to moderate, with weak dissolution in some samples. Small- and medium-sized placolith species (<3 and 3–5.5 µm, respectively) dominate most of the assemblages (Table T7). Two possible hiatuses were detected (see above) at this site.

Six Pleistocene nannofossil events defined and/or calibrated by Raffi et al. (2006 and references therein) and Flores et al. (2010) were identified in Hole U1390A (Table T6). In this site the LO of Gephyrocapsa omega (0.57 Ma; Maiorano and Marino, 2004, and references therein) was considered to better constrain the younger hiatus. The deepest samples in Holes U1390B and U1390C are younger than the first occurrence (FO) of Emiliania huxleyi (0.26 Ma) and thus precede the first hiatus recognized in Hole U1390A.

The change in abundance of large E. huxleyi (>4 µm) that characterizes Termination 1 in mid-latitude water masses in the Atlantic Ocean has been proven as a useful event by Flores et al. (2010). This change in abundance was recorded in Hole U1390A between Samples 339-U1390A-2H- 3, 75 cm, and 2H-4, 75 cm (7.37–8.87 mbsf). The FO of E. huxleyi (0.26 Ma), which marks the base of Zone NN21, was placed in Hole U1390A between Samples 22X-1, 70 cm, and 22X-2, 20 cm (189.50–190.50 mbsf). However, this event should be taken with caution because of dissolution effects and the low proportion of this species.

A possible hiatus was detected between Samples 339-U1390A-26X-2, 15 cm, and 26X-2, 23 cm (228.65–228.73 mbsf), characterized by a variation in the composition of calcareous nannofossil assemblages. The concomitant presence of Pseudoemiliania lacunosa (last occurrence [LO] at 0.46 Ma) and G. omega (LO at 0.57 Ma; Maiorano and Marino, 2004) in the latter sample allows us to place the hiatus within Zones NN20 and NN19 (i.e., between 0.26 and 0.57 Ma).

Reticulofenestra asanoi was not identified at this site. In general, the R. asanoi biohorizon (0.90–1.07 Ma) is considered a useful and globally recognized event in Pleistocene sediment. The subsequent event recognized is the LO of large Gephyrocapsa spp. (>5.5 µm) (1.24 Ma), placed between Samples 339-U1390A-32X-5, 138 cm, and 32X-6, 23 cm (292.08–292.43 mbsf), and pointing to a second hiatus at this site that covers the interval between 0.9 and 1.24 Ma.

The LO of Helicosphaera sellii (1.25 Ma) was identified between Samples 339-U1390A-36X-CC and 37X-1, 72 cm (332.63–333.02 mbsf). This event is considered diachronous (Raffi et al., 1993; Wei, 1993). However, its occurrence at this site is consistent with the ages provided by Raffi et al. (2006) for the Mediterranean Sea when compared with other calibrated events.

Planktonic foraminifers

Planktonic foraminifers were studied in all core catcher samples from Holes U1390A–U1390C. To better constrain the older hiatus and the paracme of N. pachyderma (sinistral), additional samples were analyzed from Core 339-U1390A-34X. Foraminifer abundance is, in general, abundant to dominant, and preservation is very good to good (Table T8). Lesser abundance was observed in Core 339-U1390A-34X and Samples 339-U1390A-36X-CC and 37X-CC, which consist of detrital sands (see “Lithostratigraphy”).

The planktonic foraminifer assemblages are typical for subtropical to temperate surface waters. The presence of Globigerinoides ruber (pink), Globigerinoides trilobus, and Globigerinoides sacculifer indicate warmer conditions and thus interglacial or interstadial conditions. Samples 339-U1390A-1H-CC and 339-U1390C-1H-CC are attributed to the Holocene, and Samples 339-U1390A-14X-CC, 339-U1390B-13H-CC, and 339-U1390C-13H-CC most likely correlate with marine isotope stage (MIS) 5e. In several samples, especially from the interval between Cores 3H and 9H in all three holes and Samples 339-U1390C-16H-CC through 19H-CC, Globigerina bulloides and N. pachyderma (dextral) dominate the fauna, indicating glacial conditions. Deep-dwelling foraminifers, typically Globorotalia truncatulinoides and/or Globorotalia crassaformis, were found in nearly every sample and can even reach abundances of 5%–10% (few).

Samples 339-U1390A-30X-CC; 31X-CC; 33X-CC; 34X-1, 59–61 cm; 34X-3, 59–61 cm; and 37X-CC contain few specimens of reworked Pliocene or Miocene planktonic foraminifer species, (i.e., Globorotalia margaritae, Globorotalia puncticulata, Globorotalia miotumida, and Sphaeroidinellopsis seminulina). Generally, each species is represented by just one specimen.

The only biostratigraphic event, the top of the paracme of N. pachyderma (sinistral) defined by the reappearance of this species in MIS 36 (1.21 Ma; Lourens et al., 2004; Raymo et al., 1989; Sierro et al., 2009), was observed between Samples 339-U1390A-31X-CC and 32X-CC (284.61–293.68 mbsf).

Large, heavily encrusted specimens of Neogloboquadrina atlantica (dextral) were observed in Samples 339-U1390A-36X-CC and 37X-CC (332.63–335.27 mbsf). This event was observed at other sites of this expedition, occurring at ~1.3 Ma and always within the paracme of N. pachyderma (sinistral).

Benthic foraminifers

All core catcher samples from Hole U1390A were analyzed for benthic foraminiferal assemblages (Table T9). Benthic foraminifers are generally abundant and well preserved. As at previous sites, the abundance and preservation of benthic foraminifers are related to lithology, and less abundant, moderately preserved benthic foraminiferal assemblages are associated with coarser sediments.

Most of the samples above the younger hiatus (Samples 339-U1390A-1H-CC through 25X-CC) are dominated by Brizalina dilatata, Bulimina striata gr., Cassidulina teretis, Melonis barleeanus, and Uvigerina spp., species that characterize environments with elevated organic matter flux and reduced ventilation (van Morkhoven et al., 1986; Leckie and Olson, 2003; Murray, 2006). Sample 339-U1390A-19X-CC possesses a unique composition with a very high abundance of Eubuliminella exilis (>75%), a species rarely observed in other samples from this and previous sites. Its high abundance might be related to a change in the source and the quality of the organic matter delivered to the seafloor, as this species proliferates in environments rich in fresh phytodetritus (Caralp, 1989). Strong bottom currents are indicated by elevated abundances of Trifarina angulosa in Samples 339-U1390A-17X-CC, 20X-CC, and 22X-CC through 25X-CC. In most of these samples, a parallel decrease in B. dilatata is observed.

Below the hiatus, Cibicides/Cibicidoides spp. occurs more commonly, with the highest abundances between Samples 339-U1390A-33X-CC and 38X-CC. In parallel, the abundances of Brizalina, Bulimina, Melonis, and Uvigerina species significantly decrease, pointing to improved ventilation.

The “epibenthos group,” which has been suggested as an indicator for MOW intensity in the area (Schönfeld, 1997, 2002; Schönfeld and Zahn, 2000), has generally low abundances of <5% and is most common between Samples 339-U1390A-26X-CC and 32X-CC. In contrast to previous sites, Discanomalina coronata is a regular component besides Cibicides lobatulus, Planulina spp., and Textularia pseudogramen.

The last frequent occurrence of nodosariids, pleurostomellids, and stilostomellids was recorded in Sample 339-U1390A-32X-CC. Above this level (i.e., above the older hiatus), individual shells of Siphonodosaria were identified in Samples 339-U1390A-31X-CC, 29X-CC, 28X-CC, 16X-CC, and 15X-CC. These single shells are considered allochthonous, as the corresponding planktonic foraminifers indicate reworking (Table T8). After careful consideration and comparison with age estimates from the other microfossil groups, the Stilostomella extinction (0.58–0.7 Ma) (Hayward, 2002; Kawagata et al., 2005) is placed between Samples 339-U1390A-31X-CC and 32X-CC (284.61–293.68 mbsf).

Palynology

Seven samples from Hole U1390A (Samples 1H-CC, 6H-CC, 12X-CC, 18X-CC, 24X-CC, 30X-CC, and 36X-CC) were analyzed. The lowest pollen and spore concentrations correspond to samples characterized by the highest proportion of sand (Samples 12X-CC and 36X-CC; see “Lithostratigraphy”), although the preservation is good to moderate.

The very low resolution pollen record reflects the alternating dominance of the four main plant ecological groups that characterize this region, Pinus, Mediterranean forest, semidesert, and grasslands (Fig. F21), as already documented at the previous sites for the last 1.5 m.y (see “Biostratigraphy” in the “Site U1385,” “Site U1386,” “Site U1837,” “Site U1388,” and “Site U1389” chapters [Expedition 339 Scientists, 2013c, 2013d, 2013e, 2013f, 2013g). Interestingly, the floristic composition and the proportion of each palynomorph in the uppermost sample (339-U1390A-1H-CC) is similar to those found in the levels dated between ~7.3 and 4.4 calendar k.y. BP in the Guadiana estuary (Fletcher et al., 2007). These levels are characterized by the abundance of Quercus, Taraxacum-type, Poaceae, and Isoetes spores; the low concentrations of Pinus; and the virtual absence of Ericaceae. Therefore, an age of ~6 calendar k.y. BP was assigned to 3.63 mbsf, indicating a high sedimentation rate for the mid–late Holocene interval of this sequence (Fig. F20).