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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.

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