Vegetation dynamics during the early to mid-Holocene ... - IMEP

Veget Hist ArchaeobotTable 2 Radiocarbon ages for six samples from the core BM1, NW MaltaSamplenumberLab codeDepth(cm)14 C age(year B.P.)Calibr. age(cal. year B.P.)Cal. age range/probability ()MaterialdatedBM1/64A SacA-11663 845 4563 ± 30 5120 ± 655292 ± 285055–5186 (0.52)5264–5321 (0.43)CharcoalBM1/80 Poz-42441 1005 5410 ± 40 6236 ± 60 6176–6296 (0.89) CharcoalBM1/93 SacA-11668 1117.5 6115 ± 30 6964 ± 676897–7031 (0.72) Peat7125 ± 307095–7156 (0.21)BM1/100 SacA-11669 1215 6500 ± 30 7441 ± 307362 ± 377411–7472 (0.62)7325–7399 (0.38)CharcoalBM1/121 Poz-42439 1415 6650 ± 60 7521 ± 88 7433–7609 (1) CharcoalCalibrated dates are reported as means of the 2r-ranges with highest probability. Possible age-ranges with highest probabilities (in parentheses) arealso reported as a separate column (2r-ranges). 14 C ages were calibrated by CALIB 6.1.1 based on IntCal09 calibration dataset (Reimer et al. 2009)Quercus ilex, Rhamnus lycioides ssp. oleoides and Tetraclinisarticulata, the latter being a presumed relict species(Haslam et al. 1977).Materials and methodsCoring, chronology, and stratigraphyFour cores (BM1–BM4) were recovered from the Burmarradfloodplain (NW Malta) using a percussion corer (Berettadrilling machine) in spring 2008 and 2010 (Fig. 1). The sitewas selected based on preliminary exploratory drillingsconducted during an earlier project (Gambin 2005) thatrevealed the presence of a relatively thick and continuousterrestrial-marine sediment infill. After stratigraphicaldescriptions, core BM1 (14 m long) was subsampled every5–10 cm for further pollen and sedimentological analyses.Five radiocarbon ages were obtained to construct the agedepthmodel. 14 C ages, reported in Table 2, were calibratedin Calib 6.1.1 using IntCal09 (Reimer et al. 2009). The agedepthmodel (Fig. 3) was constructed using non-Bayesianmodeling in the R-based package of CLAM (Blaauw 2010).The age-depth model shows an age-range of 8465–7763 cal.B.P. for the base of the core at 1,400 cm. However, in thisstudy, only the calibrated chronology for the interval of12–9 m has been shown (see below). This interval starts withupper estuarine dark grey silts (1,200–1,115 cm) whichsuddenly change into a fine-grained peat formed in a closedfreshwater wetland system. At about 1,105 cm, lower estuarinegrey silts replace the wetland organic deposits andcontinue up to about 975 cm where they grade into the openmarine grey shelly sands.Pollen analysisA series of tests was conducted all along the core tolocate the polliniferous sections of the sample. Thesection 1,200–900 cm presented good pollen preservationand was pollen-rich. We focused our attention on thissection with a sampling resolution of 10 cm. Extraction ofpollen grains and Non-Pollen Palynomorphs (NPPs) wasundertaken using 10 % HCl, 40 % HF, 37 % HCl andacetolysis (e.g. Moore et al. 1991). Pollen identificationwas performed with the help of the IMBE’s pollen referencecollection and the pollen atlases of Europe and NorthAfrica (Reille 1992, 1995, 1998). The Ostrya-type pollencurve may represent both Carpinus orientalis (Beug 2004)and Ostrya and the Quercus pollen curve is the sum ofQ. ilex-type and Q. pubescens-type. Dinoflagellates weredetermined by Laurent Londeix (EPOC, University ofBordeaux); NPPs were identified using Cugny (2011),Mudie et al. (2011) and Haas (1996). Pollen percentageswere calculated in TILIA and the pollen percentage diagram(Fig. 3) was constructed using TGView software(Grimm 2004–2005). In calculating pollen percentages ofupland plants i.e. trees, shrubs and herbaceous speciesgrowing on well-drained soils, aquatic and hygrophilousplants (Cyperaceae, spores, Typha/Sparganium-types) wereexcluded from the pollen sum. However, in calculating thepollen percentages of these latter plants, they were includedin the Total Pollen Sum. Hence, the final pollen diagram is asynthetic diagram in which the pollen curves calculated withtwo above methods are placed together. The pollen diagramwas subdivided into Local Pollen Assemblage Zones(LPAZs) by applying stratigraphically-constrained clusteranalysis to percentage data using CONISS software includedin the TILIA package (Grimm 1987, 2004–2005). Pollenconcentration values were also calculated by the addition ofLycopodium tablets (Stockmarr 1971) to check that thepollen percentage variations were not an artifact of lowpollen concentration values. PCA analysis was applied topollen percentages using XLSTAT v. 2009.3.02 (Addinsoft,Paris 1995–2009) and the axis 1 (18 % of variability) scoresfor different samples were plotted against the depth in thepollen diagram (Fig. 3).123