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doi:10.2204/iodp.proc.339.107.2013

Biostratigraphy

The sedimentary succession at Site U1389 dates from the Holocene to the late Pliocene (Fig. F21; Table T7), with the base age of Hole U1389E estimated at younger than 3.7 Ma. The samples are rich in planktonic and benthic foraminifers as well as calcareous nannofossils and ostracods. Only Samples 339-U1389A-35X-CC and 36X-CC and 339-U1389C-36X-CC from a sandy horizon were barren of calcareous nannofossils and planktonic foraminifers but contained a few poorly preserved benthic foraminifers. All calcareous microfossils are, in general, moderately to well preserved. Pteropod fragments are more common than at any of the previous sites and occur in nearly all samples from Cores 1H through 3H of Holes U1389A–U1389C (Table T8) and occur sporadically in the older sediment (Samples 339-U1389C-28X-CC and 339-U1389E-25R-CC, 26R-CC, 28R-6, 33R-CC, and 43R-CC.

Pollen and spores are abundant in the 16 samples analyzed in Holes U1389A and U1389E, ranging from ~8,000 and 49,000 grains/cm³, excluding the lowest sample, which contains ~2,000 grains/cm³. Pollen and spore concentrations are highest at the uppermost part of the site (Fig. F22). These values are similar to those found at Sites U1386 and U1387. Preservation of grains is good to poor in Hole U1389A and moderate to poor in Hole U1389E. The proportion of unidentifiable grains progressively increases downhole, as is the case at Site U1387. Microcharcoal particles and dinocysts were also observed.

The sedimentation rates, estimated based on the calcareous nannofossil and planktonic foraminifer bioevents (Table T7), agree well with paleomagnetic datums for the Olduvai Subchron and the Gauss/Matuyama boundary (Fig. F21; see also “Paleomagnetism”). Sedimentation rates decrease downhole and can be divided into four intervals, one of which indicates a probable hiatus. During the youngest period (0–0.46 Ma), a rate of ~40 cm/k.y. was recorded, preceded by a rate of ~30 cm/k.y. between 0.46 and 2.09 Ma.

The third sedimentation rate interval is bracketed by two planktonic foraminifer events, the first occurrence (FO) of Globorotalia inflata at 2.09 Ma and the last occurrence (LO) of Globorotalia puncticulata at 2.41 Ma. Sedimentation rate in this interval is ~5 cm/k.y., a substantial decrease from the values above and below. This unusually low value and the consistency in the values above and below this interval (Fig. F21) indicate the presence of a probable hiatus of <0.3 m.y. duration. No support for the existence of a hiatus can be given from the calcareous nannofossil data (see below). On the other hand, the succession from G. puncticulata to G. inflata with a gap of globorotaliids of this lineage in between (Core 339-U1389E-34R; Table T9) is similar to that recorded in the Mediterranean (Hilgen, 1991; Lourens et al., 2004). Distinguishing between a decrease in sedimentation rate and an hiatus is currently not possible.

For the deepest part of Site U1389, between 2.41 and <3.7 Ma, the estimated sedimentation rate is ~25 cm/k.y.

Calcareous nannofossils

We examined all core catcher samples from Holes U1389A, U1389B, U1389C, and U1389E for calcareous nannofossil biostratigraphy. Additionally, selected samples from Holes U1389A, U1389B, and U1389E were analyzed in order to constrain biohorizons, paying attention only to marker species. Calcareous nannofossil assemblages are abundant and the preservation is good to moderate, with weak dissolution in some samples (Table T10). Small placolith species (<3 µm) dominate most of the assemblages.

In total, 12 Quaternary and Neogene nannofossil datums defined and/or calibrated by Raffi et al. (2006 and references therein) and Flores et al. (2010) were identified in all holes (Table T7).

The change in abundance of large Emiliania huxleyi (>4 µm) that characterizes Termination 1 in mid- to low-latitude water masses in the Atlantic (Flores et al., 2010) was recorded between Samples 339-U1389A-1H-2, 75 cm, and 1H-3, 75 cm (2.25–3.75 mbsf); between the top of Core 339-U1389B-1H and Sample 1H-CC (0–9.72 mbsf); and between the top of Core 339-U1389C-1H and Sample 1H-CC (0–9.74 mbsf), making it possible to distinguish the onset of the Holocene in all three holes.

The FO of E. huxleyi (0.26 Ma), which marks the base of Zone NN21, was placed between Samples 339-U1389A-11H-2, 75 cm, and 11H-3, 75 cm (91.96–93.37 mbsf) and between 339-U1389C-12X-CC and 13X-CC (111.64–122.26 mbsf).

The LO of Pseudoemiliania lacunosa (0.46 Ma), considered a globally synchronous event that defines the top of Zone NN19, occurs between Samples 339-U1389A-24X-2, 74 cm, and 24X-3, 107 cm (208.73– 210.56 mbsf), and 339-U1389C-23X-CC and 24X-CC (211.52–221.12 mbsf).

The LO of Reticulofenestra asanoi (0.90 Ma) was placed between Sample 339-U1389A-36X-1, 83 cm, and 37X-1, 115 cm (322.63–332.55 mbsf), and 339-U1389C-36X-1, 80 cm, and 36X-1, 134 cm (326.9– 327.44 mbsf). The FO of R. asanoi (1.07 Ma), another significant event for the Pleistocene, was recorded between Sample 339-U1389E-5R-2, 75 cm, and 5R-3, 75 cm (360.65–362.15 mbsf). To define these biohorizons, we considered specimens of R. asanoi ≥6 µm in size.

The LO of large Gephyrocapsa spp. (>5.5 µm; 1.24 Ma) and the LO of Helicosphaera sellii were recorded between Samples 339-U1389E-7R-1, 5 cm, and 8R-1, 89 cm (377.66–387.99 mbsf). The FO of large Gephyrocapsa spp. (>5.5 µm; 1.61 Ma) was identified between Samples 339-U1389E-17R-3, 77 cm, and 17R-4, 77 cm (477.07–478.57 mbsf). The LO of Calcidiscus macintyrei (1.66 Ma) was identified between Samples 339-U1389E-20R-CC and 21R-CC (510.09–515.65 mbsf).

The LO of Discoaster brouweri defines the boundary between Zones NN18 and NN19. In Hole U1389E, the record of this species is scarce and discontinuous between Samples 339-U1389E-28R-6, 5 cm, and 35R-CC (586.78–653.74 mbsf), preventing accurate placement. Moreover, these sections are characterized by the presence of some slumped intervals (e.g., Core 339-U1389E-28R; see “Lithostratigraphy”) that can include reworked species.

Based on the planktonic foraminifer record, the possible existence of a hiatus is suggested between the FO of G. inflata (2.09 Ma) and the LO of G. puncticulata (2.41 Ma). The absence of accurate calcareous nannofossil bioevents in this interval cannot contribute to confirm the hiatus.

The LO of Discoaster pentaradiatus, marking the boundary of Zones NN17 and NN18, was identified between Samples 339-U1389E-37R-CC and 38R-CC (674.25–681.98 mbsf), indicating an early Pleistocene age.

The LO of Discoaster surculus (2.53 Ma) is used here to approximate the Pleistocene/Pliocene boundary between Samples 339-U1389E-38R-CC and 39R-CC (681.98–693.70 mbsf).

The oldest event identified at this site is the LO of Discoaster tamalis (2.8 Ma) between Samples 339-U1389E-44R-4, 5 cm, and 45R-CC (737.96–751.54 mbsf). From this depth to the base of Hole U1389E, the calcareous nannofossil assemblage is typical of the upper Pliocene, dominated by abundant small Gephyrocapsa, small and medium Reticulofenestra, and regular presence of P. lacunosa. The records of Sphenolithus spp. and Reticulofenestra pseudoumbilicus (>7 µm), which are intermittent, were interpreted as reworked. Thus, the base age of Hole U1389E is younger than the LO of these species at 3.70 and 3.82 Ma, respectively.

Planktonic foraminifers

Samples from all core catchers were analyzed in Holes U1389A–U1389C and U1389E (Tables T8, T9). No samples were taken from Hole U1389D. In Holes U1389A and U1389E, additional samples from within the cores were studied to better constrain the Holocene/Pleistocene boundary (Hole U1389A) and the position of some planktonic foraminifer events (Hole U1389E). Planktonic foraminifers are moderately to well preserved, except for Samples 339-U1389A-32X-CC, 339-U1398C-38X-CC, and 339-U1389E-22R-CC. Samples 339-U1389A-35X-CC and 36X-CC and 339-U1389C-36X-CC are devoid of planktonic foraminiferal shells, and Sample 339-U1389C-37X-CC is almost barren.

The assemblages are composed of both warm- and cold-water species. Significant constituent species of the cold-water assemblage are Neogloboquadrina pachyderma (sinistral) and Globigerina bulloides. On the other hand, the warm-water assemblage is characterized by the dominance of Globigerinoides ruber, Globigerinoides trilobus, Globigerinoides sacculifer, and Sphaeroidinellopsis seminulina, with the latter three species becoming more important in the lower Pleistocene and upper Pliocene. The dominance of G. inflata in the Pleistocene and G. puncticulata in the Pliocene sediment, as well as the presence of N. pachyderma (dextral) in the assemblages, characterizes transitional conditions from temperate to cool subtropical water masses. Other species commonly associated with the transitional water mass assemblage are Globorotalia truncatulinoides, Globorotalia crassaformis s.l., and Globogerinita glutinata.

As for the previous sites, Neogloboquadrina atlantica (dextral) was observed in samples from the mid-Pleistocene of Hole U1389E, with a continuous presence between Samples 339-U1389E-25R-CC and 9R-CC and a single earlier occurrence in Sample 31R-CC.

The occurrence of N. atlantica (sinistral) between Samples 339-U1389E-35R-CC and 40R-CC and in Sample 51R-1, 59–61 cm, was too rare to define its LO as a biohorizon. Likewise, Globorotalia miocenica was observed only in Samples 52R-5, 59–61 cm, and 64R-1, 59–61 cm, and was thus too rare to be used as biostratigraphic datum.

In the upper Pliocene samples, G. puncticulata is often present as the more inflated Globorotalia bononiensis morphotype).

Evidence of reworked foraminifers was only found in some samples and always restricted to a few specimens: one specimen of Globorotalia margaritae in Sample 339-U1389E-35R-CC; one or two specimens of G. puncticulata in Samples 23R-CC, 24R-CC, and 25R-CC; and one specimen of S. seminulina in Samples 15R-CC, 23R-CC, and 29R-CC.

In Holes U1389A–U1389C, no planktonic foraminifer event was observed because the holes only contain mid- to upper Pleistocene sediments (Fig. F21). However, 10 planktonic foraminifer events were recognized in Hole U1389E, spanning from the upper Pliocene (<3.81 Ma) to the lower Pleistocene (Table T7).

The top of the paracme of N. pachyderma (sinistral), defined by the reappearance of this species in marine isotope Stage 38 (1.21 Ma; Lourens et al., 2004; Raymo et al., 1989; Sierro et al., 2009), was observed between Sections 339-U1389E-6R-1 and 6R-CC (368.62–369.54 mbsf).

The bottom of the paracme of N. pachyderma (sinistral) is also poorly constrained because the species is absent from Samples 339-U1389E-6R-CC through 11R-4 (369.54–421.80 mbsf) and very rare in Section 12R-6 (433.73 mbsf). We consequently placed this event at this depth, although a higher resolution analysis is needed to refine its position.

The FO of G. inflata was identified between Samples 339-U1389E-33R-1, 59–61 cm, and 33R-3, 59–61 cm (627.21–630.21 mbsf). The event is very reliable because this species is very abundant and constantly present in the North Atlantic since its FO. The age of this event is 2.09 Ma (Lourens et al., 2004) and was recorded for the first time during this expedition because in the previous sites either the recovered sediments were younger in age or the FO of G. inflata was associated to a significant hiatus.

Below the FO of G. inflata, globorotaliids of this lineage are absent (Table T9) until the regularly observed specimens of G. puncticulata between Samples 339-U1389E-34R-CC and 35R-1, 59–61 cm (645.02–646.61 mbsf), in which the LO of this species was recorded. This event is also very reliable because this species, which is very abundant in the Mediterranean and northeast Atlantic until 2.41 Ma (Lourens et al., 2004), completely disappeared from this region.

G. crassaformis varies from rare to common in the lower Pleistocene. With the exception of some short increases of dextral specimens, G. crassaformis is dominantly sinistral in the upper part of the hole. A pronounced change from sinistral to dextral was observed, however, between Samples 339-U1389E-47R-CC and 48R-CC (764.48–772.41 mbsf). This event was identified in the Mediterranean (Zachariasse et al., 1989) and has been astronomically dated at 2.99 Ma (Berggren et al., 1995; Lourens et al., 2004; L.J. Lourens, pers. comm., 2012) (Table T7).

The LO of Dentoglobigerina altispira (3.17 Ma) was observed between Samples 339-U1389E-54R-CC and 55R-1, 29–31 cm (830.21–838.21 mbsf). In general, this species is rare in Hole U1389E. Support for placing the LO at this level at Site U1389 comes from evidence in the Mediterranean. There, in the Punta Piccola section in Sicily, the LO of D. altispira was found immediately above the LO of S. seminulina during an interval of dextral coiling G. crassaformis (Zachariasse et al., 1989). Although the LO of D. altispira coincides with the LO of S. seminulina in our low-resolution study at Site U1389, both occurred during an interval with dominantly dextral coiling G. crassaformis (Table T9).

The LO of S. seminulina (3.19 Ma; Lourens et al., 2004) was found at the same level as the LO of D. altispira (i.e., between Samples 339-U1389E-54R-CC and 55R-1, 29–31 cm; 830.21–838.21 mbsf).

The top of the temporal disappearance of G. puncticulata (3.31 Ma; Lourens et al., 2004) was recorded between Samples 339-U1389E-57R-3, 58–60 cm, and 57R-5, 59–61 cm (860.70–863.74 mbsf).

The bottom of the temporary disappearance of G. puncticulata (3.57 Ma; Lourens et al., 2004), was identified between Samples 339-U1389E-65R-1, 59–61 cm, and 64R-6, 49–54 cm (932.13–934.61 mbsf).

Sample 339-U1389E-70R-CC (982.78 mbsf), at the base of Hole U1389C, contains many specimens of G. puncticulata but no G. margaritae, indicating that the age of this sediment is younger than 3.81 Ma (i.e., the age of the LO of G. margaritae in the Mediterranean and northeast Atlantic [Lourens et al., 2004]). The presence of some specimens of Globorotalia hirsuta (dextral) in this sample suggests that this sediment was deposited immediately above the LO of G. margaritae, in accordance with observations in equivalent sections offshore northern Morocco (Sierro, unpubl. data).

Benthic foraminifers

All core catcher samples from Holes U1389A and U1389E were analyzed for benthic foraminiferal assemblages (Table T11). Additionally, Samples 339-U1389B-21X-CC through 38X-CC were evaluated for the “Stilostomella extinction.” As with previous sites, the abundance and preservation of benthic foraminifers are related to lithology, and major changes in benthic foraminiferal assemblages correspond well with lithologic units. Benthic foraminifers are generally abundant. Moderately to well preserved assemblages preferentially occur in the upper and lower portions of the succession, whereas moderate to poor preservation occurs in Samples 339-U1389A-35X-CC through 39X-CC and 339-U1389E-22R-CC through 50R-CC.

Based on the revealed benthic foraminiferal assemblages, three intervals can be distinguished in the succession that correspond well to lithologic Subunits 1A–1E (see “Lithostratigraphy”):

1. The interval between Samples 339-U1389A-1H-CC and 34X-CC is characterized by benthic assemblages composed of Brizalina, Bulimina, Cassidulina, Melonis, and Uvigerina species that characterize environments with increased organic matter flux and reduced ventilation (van Morkhoven et al., 1986; Leckie and Olson, 2003; Murray, 2006). Occasional peaks in Cibicidoides spp. record episodes of increased bottom water ventilation (e.g., Samples 339-U1389A-22X-CC and 31X-CC). Overall, these assemblages are very similar to those from Pleistocene contourite deposits at other sites. The “epibenthos group,” suggested as an indicator for MOW intensity in the area (Schönfeld, 1997, 2002; Schönfeld and Zahn, 2000), shows low abundances of <5%. However, Trifarina angulosa, which is also related to strong bottom currents, commonly shows elevated abundances.

2. Between Samples 339-U1389A-35X-CC and 39X-CC and 339-U1389E-2R-CC and 39R-CC, the abundance of Cibicidoides spp. generally increases, whereas the taxa characteristic of the first interval decrease, especially Uvigerina. Transport from the shelf is increased during this interval, corresponding to the increasing amount of turbiditic layers in this interval (see “Lithostratigraphy”). It can be noted that the deep-infaunal foraminifer Globobulimina affinis that commonly occurs in dysoxic deep-sea environments was observed frequently in this interval. This species is able to process low-quality organic matter more efficiently than other foraminifers; thus its occurrence might also reflect organic matter input from the shelf. The epibenthos group shows increased abundances, mainly caused by the more frequent Cibicides lobatulus (mainly in Samples 339-U1389A-37X-CC and 339-U1389E-18R-CC). In parallel, the abundance of Trifarina spp. decreases compared to its abundance in Assemblage 1.
   Within this interval, the first appearance of Hyalinea balthica, an indicator for cold-water masses (Bayliss, 1969; van Morkhoven et al., 1986), was recorded between Core 339-U1389E-13R-CC and Section 14R-CC shortly after the Mid-Pleistocene Transition. This pattern is very similar to previous Sites U1386 and U1387 and corresponds well with Mediterranean records. It also coincides with the disappearance of Siphonina tubulosa.

3. Samples 339-U1389E-40R-CC through 70R-CC yield an assemblage of Cibicidoides, Melonis, Brizalina, and Uvigerina that shows similarities to Pliocene sediment at Sites U1386 and U1387. Cassidulina laevigata/teretis, commonly occurring in boreal waters of the North Atlantic during the middle–late Pliocene and the Pleistocene, becomes rare in this interval. In parallel, the abundance of S. tubulosa increases and peaks between Samples 339-U1389E-55X-CC and 70X-CC. This epifaunal species has been described from warm and oxygen-depleted, upper–middle bathyal environments (e.g., Szarek et al., 2007). Thus, the inverse trends in C. laevigata/teretis and S. tubulosa are potentially related to the mid-Pliocene climate optimum. The epibenthos group consists of C. lobatulus and Planulina spp. and shows an average abundance of ~5%.

The Stilostomella extinction event cannot be used as a reliable biostratigraphic datum at Site U1389. Nodosariids, pleurostomellids, and stilostomellids occur commonly between Samples 339-U1389E-5R-CC and 70R-CC. Above this level, individual shells have been identified in Samples 339-U1389A-39X-CC, 37X-CC, and 19X-CC. Hole U1389C shows no occurrences in the studied interval (Sections 339-U1389C-21X-CC through 38X-CC). The comparison with the age constraints from calcareous nannoplankton and paleomagnetic measurements suggests that the extinction occurs 200–300 k.y. earlier at this site compared to the other sites and previous studies (0.58–0.7 m.y.) (Hayward, 2002; Kawagata et al., 2005). The factors responsible for this diachroneity remain uncertain.

Ostracods

Ostracods were examined from the uppermost nine core catcher samples of Hole U1389A (4.25–81 mbsf) and are most abundant in Samples 339-U1389A-1H-CC through 3H-CC. Diversity is relatively high, with 36 genera recognized (Table T12). The overall ostracod assemblage is composed of a mix of upper bathyal (i.e, Cytheropteron, Argilloecia, Krithe, Cytherella, Henryhowella, Pseudocythere, and Parakrithe) and circalittoral (i.e., Paradoxostoma, Semicytherura, Loxoconcha, Aurila, Buntonia, Pterigocythereis, Callistocythere, Hiltermannicythere, Urocythereis, Xestoleberis, Caudites, and Leptocythere) taxa (Carbonel, 1985; Ruiz et al., 1997, 2008). Notably, Sample 339-U1389A-1H-CC also contains single specimens of freshwater genera Ilyocypris and Potamocypris (Ruiz et al., 2000; Alvarez Zarikian et al., 2008; Faranda and Gliozzi, 2008). The mix of bathyal, shelf, and littoral taxa in the youngest part of the record suggests that estuarine sediments can be transported today by river plumes far into the Gulf of Cádiz.

Palynology

Seven samples from Hole U1389A (Samples 1H-CC, 6H-CC, 12X-CC, 18X-CC, 25X-CC, 31X-CC, and 37X-CC) and nine samples from Hole U1389E (Samples 4R-CC; 10R-CC; 16R-1, 0–5 cm; 22R-CC; 28R-6, 0–5 cm; 32R-CC; 41R-CC; 51R-CC; and 61R-1, 0–5 cm) were analyzed. The lithology of these samples varies from clay to silty sand, and no correlation was observed between the degree of preservation and the nature of the sediment. Good, moderate, and poorly preserved pollen grains were found in clay sediment. Pinus is well represented in the upper 400 m of the sequence, with the maximum abundance in Sample 339-U1389A-12X-CC (Fig. F22; Table T13), and is virtually absent below this level (Samples 339-U1389E-16R-1, 0–5 cm; 22R-CC; 28R-6, 0–5 cm; 32R-CC; 41R-CC; 51R-CC; and 61R-1, 0–5 cm), although some of the corroded pollen of conifers likely belong to the Pinus genus. The same feature is observed at the previous sites and indicates an age older than 1.6 Ma.

The pollen record covering the last 1.7 m.y. reflects the alternating dominance of the four main plant ecological groups that characterize this region, Pinus, Mediterranean forest, semidesert, and grasslands, as already documented at the previous sites (see “Biostratigraphy” in the “Site U1385,” “Site U1386,” and “Site U1387” chapters [Expedition 339 Scientists, 2013c, 2013d, 2013e]). Samples below 600 mbsf, dated older than 2 Ma, have the highest unidentifiables/total pollen and spores ratios. Samples 339-U1389E-28R-6, 0–5 cm, 32R-CC, 41R-CC, and 51R-CC are dominated by the pollen of Taraxacum-type, which is very resistant to corrosion and, additionally, easy to identify when damaged. This pollen morphotype, associated with steppe assemblages in well-preserved pollen samples, is generally overrepresented in pollen assemblages that are severely corroded, such as those observed in Greek Holocene offshore sediments (Bottema, 1990). In contrast, Sample 339-U1389E-61R-1, 0–5 cm, is dominated by corroded pollen grains of conifers. High proportions of unidentifiable pollen of conifers are a common feature in Pliocene sequences of southwestern Iberia (Jiménez-Moreno et al., 2010). The replacement of the highest proportions of Taraxacum-type pollen by the highest ratio of corroded conifers pollen occurs at this site below 820 mbsf, dated at ~3.31 Ma. The same feature is recorded at Site U1387 below 700 mbsf and dated older than 4.5 Ma.

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