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doi:10.2204/iodp.proc.339.102.2013 BiostratigraphyPaleontologyPaleontological studies were based on semiquantitative analyses of nannofossil and planktonic foraminifer assemblages as well as benthic foraminifer and ostracod associations. In addition, the pollen and microcharcoal particle content in sediment was analyzed and the presence of pteropod shells was noted. Nannofossil and planktonic foraminifer assemblages can be used as indicators for surface water conditions, like sea-surface temperature and productivity (e.g., Colmenero-Hidalgo et al., 2004; Baumann et al., 2005; Narciso et al., 2006; Kucera, 2007; Salgueiro et al., 2010), to identify past surface water variations. Aragonitic pteropod shells are preserved in sediments during specific time intervals (Herman, 1971), such as the layer dated at 19.1 calendar k.y. before present in the Gulf of Cádiz (Voelker et al., 2006). Pteropod assemblages are found to be useful for inferring oceanographic circulation and ventilation conditions at intermediate depth. Changes in abundance variation and preservation condition of their assemblages are related to hydrographic parameters like salinity, temperature, and oxygen conditions, as well as the aragonite saturation state of deep water (e.g., Almogi-Labin et al., 1986; Gerhardt et al., 2000; Singh et al., 2005). They are frequent north of the Azores Front (Schiebel et al., 2002), which during the Last Glacial Maximum extended into the Gulf of Cádiz (Rogerson et al., 2004). By contrast, variations in the benthic foraminifer and ostracod assemblages are very useful as proxies for deepwater circulation since they are very sensitive to bottom water conditions, such as food availability, oxygen content, and other physichemical properties (e.g., Murray, 2006). In particular, variations in the benthic assemblages along the Iberian continental margin may have been driven by the interplay between surface productivity and changes in the flow intensity of the prevailing deep water (i.e., North Atlantic Deep Water, Antarctic Bottom Water, or Mediterranean Outflow Water) (e.g., Schönfeld and Zahn, 2000). The information about the composition of the planktonic and benthic foraminifer assemblages will be very useful to plan future stable isotope studies, in particular, to select the most appropriate species based on their occurrence in the different sites. Pollen and microcharcoal content can be used to explore past changes in vegetation and fire regime and, therefore, in atmospheric circulation, air temperature, and precipitation on the Iberian Peninsula. So far such changes have been reported at orbital and millennial timescales for the last 425 k.y. (e.g., Daniau et al., 2007; Sánchez Goñi et al., 2008; Desprat et al., 2005; Naughton et al., 2009; Margari et al., 2010). BiostratigraphyPreliminary ages were assigned primarily based on core catcher samples. Additional samples taken within the cores were examined when a more refined age determination was required. Calcareous nannofossil and foraminifer age events from the late Miocene to Quaternary were estimated by correlation to the geomagnetic polarity timescale (GPTS) of Lourens et al. (2004). Nannofossil and planktonic foraminifer events, zones, and subzones are summarized in Figure F11. The following terminology was applied for each group:
The concept of acme (dominance interval) and paracme (absence interval) has been also applied. The Pliocene/Pleistocene boundary has been formally established at 2.588 Ma at the boundary between the Piacenzian and Gelasian, located just above the Matuyama/Gauss magnetic reversal within marine isotope Stage 103 (Gibbard et al., 2010). The boundary can be approximated by the LO of Discoaster surculus (2.53 Ma) and the LO of Globorotalia puncticulata (2.41 Ma) (Fig. F11). The Miocene/Pliocene boundary is a remarkable event in the Mediterranean because it marks the Pliocene flooding after the Messinian salinity crisis, astronomically dated at 5.33 Ma (Hilgen, 1991), and the recovery of open-marine deep-sea microfaunas in the Mediterranean basins. However, its identification in the Atlantic is problematic because no major environmental change occurred in this area at that time. The location of this boundary is not well constrained because no bioevent has been identified in this time interval. Nevertheless, the biohorizons of the FO of Ceratolithus acutus and the LO of Discoaster quinqueramus, occurring at 5.34 and 5.54 Ma, respectively, may be used to approximate the boundary in the Atlantic. These events, however, are not valid for the Mediterranean because of the restricted connection between the Atlantic and the Mediterranean. Details of the shipboard methods are described below for each microfossil group. Calcareous nannofossilsBioevent ages were assigned based on the occurrence of calcareous nannofossils (presence, absence, or dominance) in core catcher samples and in selected sections. The calibration of the identified events was derived mainly from Raffi et al. (2006). Additionally, Martini (1971) and Okada and Bukry (1980) standard zonal schemes were adopted (Fig. F11; Table T2). The change in abundance of the large Emiliania huxleyi (>4 µm), that characterizes Termination 1 in mid- to low-latitude water masses in the northeast Atlantic Ocean (Flores et al., 2010), was utilized. Gephyrocapsa species are grouped in several size categories. Specimens <3 µm, mainly Gephyrocapsa ericsonii and Gephyrocapsa aperta, are classified as “small Gephyrocapsa.” Specimens of Gephyrocapsa muellerae and Gephyrocapsa margerelii, as well as other identified specimens in the 3–5.5 µm size range, are referred to as “medium Gephyrocapsa.” The “large Gephyrocapsa” category includes forms >5.5 µm. Gephyrocapsa oceanica is divided into G. oceanica >5 µm and G. oceanica <5 µm. Reticulofenestra specimens were also considered following a size concept. Reticulofenestra pseudoumbilicus is divided into R. pseudoumbilicus >7 µm and R. pseudoumbilicus 5–7 µm. Reticulofenestra haqii and Reticulofenestra minutula are considered “medium Reticulofenestra,” ranging between 3 and 5 µm. Forms <3 µm are “small Reticulofenestra,” mainly corresponding to Reticulofenestra minuta. Reticulofenestra asanoi is divided into R. asanoi >6 µm and R. asanoi <6 µm. Morphometric subdivision within Calcidiscus leptoporus s.l. and Coccolithus pelagicus s.l. complexes are used according to the taxonomy of Klejine (1993), Knappertsbusch et al. (1997), Steel (2001), Geisen et al. (2002), Quinn et al. (2003, 2004), and Parente et al. (2004). Otherwise, taxonomic concepts for Neogene taxa were adopted from Perch-Nielsen (1985). The magnetostratigraphy for the Cenozoic is based on Lourens et al. (2004). ForaminifersPreliminary ages were assigned based on the occurrence of planktonic foraminifers (presence, absence, and acme) in core catcher samples. Biostratigraphic events were derived mainly from Lourens et al. (2004). Additional datums are adopted from Weaver and Clement (1987), Chaisson and Pearson (1997), Krijgsman et al. (2004), Berggren et al. (1995), Hilgen (1991), Serrano et al. (1999), and Sierro (unpubl. data) (Fig. F11; Table T3). We use bioevent names as reported by the previous authors. Globorotalia conomiozea and Globorotalia miotumida are grouped together under the name of the G. miotumida group. In the Miocene, the Globorotalia menardii group also includes Globorotalia plesiotumida and Globorotalia merotumida following Sierro et al. (1993). Globorotalia crassaformis comprises the two subspecies G. crassaformis hessi and G. crassaformis ronda. Globigerinoides extremus includes Globigerinoides obliquus because it is difficult to distinguish these two species in Pliocene sediments from the Atlantic and Mediterranean regions. Globigerinella calida and Globogerinella obesa are grouped as well. For abundance estimates, Neogloboquadrina acostaensis is combined with Neogloboquadrina pachyderma, and the nomenclature of N. pachyderma (dextral) instead of Neogloboquadrina incompta is applied. Otherwise, taxonomic concepts for Neogene taxa are adopted from Kennett and Srinivasan (1983). Ages for the magnetic polarity reversals are based on Lourens et al. (2004). Benthic foraminifers provide limited biostratigraphic age control. Whenever possible, the “Stilostomella extinction” was recorded, during which a high number of deep-sea foraminifer species of Stilostomellidae, Pleurostomellidae, and Nodosariidae disappeared from the global ocean. Previous studies demonstrate that a pulsed decline in these foraminiferal groups starts at ~1.2 Ma, and that the final Stilostomella extinction datum occurs globally between 0.7 and 0.58 Ma (e.g., Hayward, 2002; Kawagata et al., 2005). PaleoceanographyBenthic foraminifersBenthic foraminifers from core catcher samples were primarily used to determine past changes in oceanographic conditions (Murray, 2006). To record changes in current velocity, the abundance of suspension-feeding benthic foraminifers was evaluated (“epibenthos group”; Schönfeld, 1997, 2002; Schönfeld and Zahn, 2000). Taxonomic assignments on the generic level follow Loeblich and Tappan (1988) with updates from Hayward (2002). OstracodsOstracods are small bivalved crustaceans that are commonly preserved as fossils in the ocean floor at depths shallower than the calcium carbonate compensation depth (CCD) and lysocline. Like benthic foraminifers, ostracods are used to reconstruct past environmental and oceanographic conditions because their distribution is controlled by physical and chemical characteristics of bottom water (Dingle and Lord, 1990; Corrège, 1993; Ayress et al., 1997; Cronin et al., 1999; Alvarez Zarikian et al., 2009; Yasuhara et al., 2009a). During Expedition 339, ostracods were studied from most sites and were identified using taxonomic assignments by Whatley and Coles (1987), Coles and Whately (1989), Alvarez Zarikian (2009), and Yasuhara et al. (2009b). Sample preparation methodsCalcareous nannofossilsSamples were prepared following the standard smear slide technique with Norland optical adhesive. Calcareous nannofossils were examined with a Zeiss polarized microscope at 1000× magnification. Preservation includes effects of dissolution and overgrowth. Preservation of calcareous nannofossils was categorized as
Total abundance of calcareous nannofossils was categorized as
Abundances of individual taxa or groups of calcareous nannofossils were categorized as
Foraminifers and ostracodsFrom each core catcher, 20–30 cm3 of sediment was analyzed for planktonic and benthic foraminifers and ostracods. Unlithified sediment samples were soaked in tap water and washed over a 63 µm sieve. Semilithified material was soaked in a 3% H2O2 solution for a few minutes before washing. In addition, mudline samples were taken from most holes and analyzed for benthic foraminifers and ostracods. Mudline samples were collected by emptying the sediment/water material from the top core liner of each hole into a bucket. Tests using Rose Bengal staining confirmed the presence of some living ostracods and benthic foraminifers in the mudline samples. Washed samples were dried at 60°C. The dried residue (>63 µm size fraction) was split for planktonic (25%) and benthic foraminifer (75%) assemblage studies. The samples were analyzed under a ZEISS Discovery V8 and ZEISS Stemi SV11 stereomicroscope, respectively. In order to avoid contamination between successive samples, sieves used for wet sieving were cleaned in an ultrasonic bath for several minutes, and those used for dry sieving were cleaned with compressed air. Planktonic foraminiferal abundance in the >150 µm fraction in relation to the total residue of each sample was categorized as
Benthic foraminiferal abundance in samples of the >63 µm size fraction is registered as
Ostracods were examined from the >150 µm fraction of each sample, and their abundance in relation to the total residue was recorded as
Relative abundance was characterized as
Pteropod abundance in the >150 µm fraction in relation to the total residue of each sample was categorized as
Preservation includes the effects of diagenesis, epigenesis, abrasion, encrustation, and/or dissolution. Preservation of planktonic and benthic foraminifers and ostracods was categorized as
PalynologyPollen, microcharcoals, dinoflagellate cysts, and other palynomorphsPalynological sample preparations yielded several types of organic-walled microfossils (i.e., palynomorphs) that include mainly dinoflagellate cysts (dinocysts), pollen, microcharcoal particles, spores from terrestrial plants, and organic linings of foraminifers. During Expedition 339, all palynomorphs were investigated with primary focus on pollen grains as paleoecological, paleoclimatic, and rough biostratigraphic indicators. A number of studies have documented the most abundant pollen morphotypes in northwestern and central Europe for the Miocene, Pliocene, Pleistocene, and Holocene (Traverse, 1988), in the Mediterranean region for Pliocene–Pleistocene (Suc, 1984), and, more recently, from the Iberian Peninsula for the Miocene–Pliocene (Jiménez-Moreno et al., 2010) and the Mid-Pleistocene Transition (MPT), from ~1 to 0.8 Ma (Joannin et al., 2011). The Pliocene vegetation of the southwestern part of this region, the area addressed by this expedition, was dominated by Cathaya, Engelhardtia, Sequoia, Myrica, and Taxodium; Ericaceae and Mediterranean xerophytes such as Olea, Phillyrea, Cistus, Rhamnaceae, and evergreen Quercus were also significantly represented. During the MPT, the most common taxa were deciduous Quercus, Ericaceae, and high- and mid-altitude conifers such as Cedrus, Abies, Tsuga, and Picea. Additionally, many studies (e.g., Lézine and Denèfle, 1997; Sánchez Goñi et al., 1999, 2000, 2008, 2009; Fletcher et al., 2007; Roucoux et al., 2006; Margari et al., 2010) have documented the most frequent pollen morphotypes from the late mid-Pleistocene (~0.425 Ma) to the Holocene in this region. On the basis of these studies, the analysis of the pollen content may allow us to roughly assign sediment to one of these epochs. However, the distinction between mid-Pleistocene, late Pleistocene, and Holocene will remain problematic, as the same Mediterranean and semidesert pollen morphotypes (deciduous and evergreen Quercus, Artemisia, Chenopodiaceae, and Ephedra) are common during these time intervals (Table T4). Sample preparation methodsApproximately 1–3 cm3 of sample was processed using a simplified palynologic treatment, avoiding HF treatments. The procedures included sieving through 100 µm mesh to discard coarse material. The fraction <100 µm was treated first with cold and then with warm HCl (30%) to remove carbonates. The residue was sieved again through a 10 µm mesh using a magnetic agitator plate to eliminate clay and fine silt particles. To concentrate palynomorphs, quartz particles were eliminated by applying the watch-glass procedure. The final residue was mounted between slides and coverslides with bi-distilled glycerine. Tablets of Lycopodium spores with known concentration (20,848 spores/tablet), referred to as exotics in the table, were included in the sample at the beginning of the preparation to allow a concentration calculation. The slides were examined on a Zeiss Axioplan microscope with magnification ranging from 200× to 500×. Taxonomic identifications were verified at 1000× magnification. Abundances are reported as
Special attention was given to pollen, grains of which were counted and identified to the genus or type within genus level when possible. Preservation of pollen grains, and palynomorphs in general, was determined qualitatively and reported as
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