Geological Survey of Finland, Special Paper 46 - arkisto.gsf.fi
Geological Survey of Finland, Special Paper 46 - arkisto.gsf.fi
Geological Survey of Finland, Special Paper 46 - arkisto.gsf.fi
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<strong>Geological</strong> <strong>Survey</strong> <strong>of</strong> <strong>Finland</strong>, <strong>Special</strong> <strong>Paper</strong> <strong>46</strong><br />
Leili Saarse, Jüri Vassiljev, Avo Miidel and Eve Niinemets<br />
Fig. 3. Distribution <strong>of</strong> radiocarbon dates with error bars. The blue line marks the age <strong>of</strong> the lower limit <strong>of</strong> the buried organic beds<br />
(cal BP), red line – the age <strong>of</strong> the upper limit. The bold black line shows water level changes in the surroundings <strong>of</strong> Pärnu (after<br />
Veski et al. 2005). The age <strong>of</strong> the different phases <strong>of</strong> the Baltic Sea basin according to Andrén et al. (2000). (BIL = Baltic Ice<br />
Lake).<br />
has been dated in 22 localities and a total <strong>of</strong> 66<br />
14 C dates are available (Fig. 3; Saarse et al. 2006,<br />
Talviste et al. 2006). Uncalibrated dates range from<br />
8,570±150 (Ta-2843) to 5,520±100 (Tln-178). Obviously,<br />
this is due to different factors as radiocarbon<br />
dates depending on the material analysed (wood,<br />
seeds, bulk organic matter, insoluble or soluble fraction),<br />
its preservation and availability to weathering,<br />
contamination with older carbon or younger rootlets<br />
(Olsson 1986, Wohlfarth et al. 1998). Wood, peat<br />
and seeds from locations 27, 28 and 35 (Fig. 1a),<br />
all connected with the Ancylus Lake development,<br />
were subjected to conventional and AMS radiocarbon<br />
dating. It was determined that the dates from<br />
the peat were older than those from wood and seeds<br />
at the same depth (Veski 1998). Several sites (5, 11,<br />
21, 31, 70; Figs. 1a, b) were re-examined. The new<br />
14 C dates obtained are commonly older than the previous<br />
ones and more consistent with pollen stratigraphy<br />
(Veski 1998). One reason for incorrect dates<br />
could be the preservation <strong>of</strong> samples (not kept in a<br />
refrigerator) and the time span between the collection<br />
and dating, which in some cases was formerly<br />
more than one year.<br />
According to the re-examined radiocarbon dates,<br />
90<br />
the Ancylus Lake transgression started about 10,800<br />
cal BP and culminated ca 300–500 years later.<br />
Around 10,100 cal BP, a rather rapid regression <strong>of</strong><br />
up to 30 m (Raukas et al. 1996) followed in the areas<br />
<strong>of</strong> rapid uplift. Buried organic deposits <strong>of</strong> Ancylus<br />
age are mostly characterised by the maximum <strong>of</strong><br />
Pinus pollen (Fig. 4). This was the main reason why<br />
the Ancylus transgression in Estonia was estimated<br />
to be about 1,000 years younger (Kessel & Raukas<br />
1979) than in neighbouring countries. According to<br />
radiocarbon dates, the Litorina transgression started<br />
about 8,300–7,800 cal BP and culminated at different<br />
times in different regions, <strong>fi</strong> rst in the areas<br />
<strong>of</strong> rapid uplift (Kessel & Raukas 1984, Miettinen<br />
2002). Pollen spectra <strong>of</strong> the Litorina Sea buried organic<br />
strata differ considerably between sites, still<br />
showing an af<strong>fi</strong> liation to the Atlantic chronozone.<br />
Comparisons <strong>of</strong> shore displacement curves with<br />
the positions <strong>of</strong> ancient settlements (Fig. 5) do not<br />
support the idea <strong>of</strong> multiple Litorina transgressions.<br />
However, this does not rule out smaller sea-level<br />
changes caused, for example, by stormy waves.<br />
Detailed bio- and chronostratigraphic analyses are<br />
needed to study the character <strong>of</strong> Litorina transgression<br />
more precisely.