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doi:10.2204/iodp.proc.339.106.2013

Biostratigraphy

Sediments recovered at Site U1388 include silty sands and sands (see “Lithostratigraphy”). Marine microfossil and nannofossil abundance was therefore lower than at the previous sites. Several samples are barren or almost barren, especially of foraminifers. Preservation, on the other hand, was often very good to good, with only few samples showing moderate preservation. A rare occurrence of pteropods was observed in Sample 339-U1388B-22X-CC. Ostracods were not studied at Site U1388, and only two samples from Hole U1388B were analyzed for pollen. The total pollen and spores concentrations were similar to those from previous Sites U1386 and U1387, ranging between 15,000 and 34,000 grains/cm³. The preservation was moderate to poor. Microcharcoal particles and dinocysts were also observed.

The deepest reliable biostratigraphic event is the last occurrence (LO) of Pseudoemiliania lacunosa (0.46 Ma), placed at 170 mbsf in Hole U1388B (Table T4). The estimated sedimentation rate between this nannofossil event and the one above is 60 cm/k.y. If this sedimentation rate is extrapolated to the base of Hole U1388B, the basal age is ~0.56 Ma, which is in good agreement with the absence of the benthic foraminifer “Stilostomella extinction” event occurring between 0.58 and 0.70 Ma. The Holocene/Pleistocene boundary could not be defined, but based on the planktonic foraminifer assemblage, Sample 339-U1388A-1H-CC likely dates from the Holocene.

Calcareous nannofossils

We examined all the core catcher samples from Holes U1388A–U1388C for calcareous nannofossil biostratigraphy. Calcareous nannofossil assemblages are abundant to rare, with the exception of Sample 339-U1388B-9X-CC, which is barren. Preservation is moderate, with the presence of dissolution and overgrowth in some samples. Small placolith species (<3 µm) dominate most of the assemblages (Table T5).

Two Pleistocene nannofossil datums defined and/or calibrated by Raffi et al. (2006 and references therein) were identified in all holes (Table T4).

The FO of Emiliania huxleyi (0.26 Ma), which marks the base of Zone NN21, was placed between Samples 339-U1388B-6X-CC and 7X-CC (47.47–56.14 mbsf). However, this event should be taken with caution because of dissolution effects and the low proportion of this species. The LO of P. lacunosa (0.46 Ma), considered a globally synchronous event that defines the top of Zone NN19, occurs between Samples 339-U1388B-18X-CC and 19X-CC (162.82–178.02 mbsf).

Planktonic foraminifers

The core catcher samples from Site U1388 contain high amounts of lithic grains (commonly in the fine sand range; Table T6). Therefore, planktonic foraminifer abundance is relatively low (abundant to present). Foraminifer abundance exceeds 30% only in Sample 339-U1388B-2X-CC. Three samples from Hole U1388B are barren, and four additional samples are almost barren. Preservation is often very good, revealing pristine foraminifer shells. Three samples (339-U1388B-4X-CC, 17X-CC, and 19X-CC) show only moderate preservation. The planktonic foraminifer assemblage is typical for this region, with species linked to temperate to subtropical waters. Similar to the previous sites, the assemblages are dominated by Globigerina bulloides, Neogloboquadrina pachyderma (dextral), and Globorotalia inflata. Orbulina universa, Globorotalia truncatulinoides, and Globigerinella siphonifera contribute regularly to the fauna. Sample 339-U1388A-1H-CC contains Globigerinoides trilobus and Globigerinoides sacculifer and therefore most likely dates from the Holocene.

Benthic foraminifers

Samples 339-U1388A-1H-CC, 339-U1388B-1H-CC through 24X-CC, and 339-U1388C-2R-CC through 4R-CC were analyzed for benthic foraminiferal assemblages (Table T7). As with Sites U1386 and U1387, the abundance and preservation of benthic foraminifers is related to lithology, and higher abundance and well-preserved benthic foraminifers are observed in finer sediments. The abundance of benthic foraminifers fluctuates from rare to highly abundant. Samples 339-U1388B-5X-CC and 9X-CC and 339-U1388B-18X-CC are barren. In most of the samples that revealed foraminifers, benthic assemblages are moderately to well preserved, except for Samples 339-U1388B-4X-CC and 7X-CC.

The benthic foraminiferal fauna is mainly composed of species of Brizalina, Bulimina, Cassidulina, Cibicidoides, Globobulimina, Sphaeroidina, and Uvigerina in varying proportions. In general, an upper bathyal environment is indicated. Transport from the shelf, indicated by Ammonia beccarii, Asterigerinata planorbis, and Elphidium spp., occurs sporadically and is mainly restricted to the upper part of the succession. Two major assemblages can be distinguished that suggest variations in ventilation and/or MOW current strength and that alternate throughout the succession:

Assemblages composed of Brizalina dilatata, Bulimina aculeata, Cassidulina laevigata/teretis, and Sphaeroidina bulloides characterize environments with increased organic matter flux and reduced ventilation (van Morkhoven et al., 1986; Leckie and Olson, 2003; Murray, 2006). Peak abundances of Brizalina spp. (Sample 339-U1388B-12X-CC, 14X-CC, and 20X-CC) indicate maxima in oxygen depletion of bottom water related to enhanced input of organic matter and/or a well-stratified water column.

Assemblages with high abundances of Cibicides/Cibicidoides spp. and Uvigerina spp. (Samples 339-U1388B-3X-CC, 7X-CC, 15X-CC, 21X-CC through 24X-CC, and 339-U1388C-2R-CC through 4R-CC) indicate increased ventilation, potentially related to an increase in MOW current strength. Within some of these assemblages, the “epibenthos group,” suggested as an indicator for MOW intensity in the area (Schönfeld, 1997, 2002; Schönfeld and Zahn, 2000), shows abundances of >5%. The exceptionally high abundance of Cibicides lobatulus in Sample 339-U1388B-3X-CC might be related to a peak in MOW strength close to the exit of the Strait of Gibraltar.

The Stilostomella extinction event was not recognized at Site U1388, thus suggesting that the deposits are younger than 0.58–0.7 Ma (Hayward, 2002; Kawagata et al., 2005). However, in Sample 339-U1388B-2X-CC, several moderately well preserved tests of Pleurostomella alternans, Siphonodosaria ketienziensis, and Siphonodosaria subtertenuata were found, which are absent in all other samples. As the same sample yields very high abundances of reworked early Pleistocene nannofossils, we consider the foraminiferal tests reworked too.

Palynology

Samples 339-U1388B-2X-CC and 14X-CC were analyzed for palynology. The main pollen types found at this site, deciduous and evergreen Quercus, Olea, Ericaceae, Chenopodiaceae, Artemisia, Taraxacum-type, and Poaceae (Table T8), are those already observed at the previous Sites U1386 and U1387 (see “Palynology” in the “Site U1386” chapter [Expedition 339 Scientists, 2013b] and “Palynology” in the “Site U1387” chapter [Expedition 339 Scientists, 2013c]). The first sample is characterized by poorly preserved pollen morphotypes and, as is normal for such samples, an abundance of Taraxacum-type pollen grains. The sample below, Sample 339-U1388B-14X-CC, is composed of an important fraction of well-preserved pollen grains dominated by semidesert elements, mainly Artemisia and Chenopodiaceae, indicating a period of arid and cold conditions in the close continents between 0.26 and 0.46 Ma (Table T4).

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