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Kirjeldus

From Raukas & Kajak (1997):

The name of the formation was proposed by Kajak et al. in 1976 after the Järva County in central Estonia where a typical grey till of the last glaciation is widespread in the drumlins and lowland near the Town of Paide. The Järva Formation is correlated with the Nemunas Formation in Lithuania, the Baltia in Latvia, the Valdaian Stage in Russia and the Weichselian in Western Europe. The Vääna-Jõesuu (13-70 m) and Kitse boreholes (0-31.1 m) were chosen for stratotype sections in northern and southern Estonia, respectively (Raukas et al. 1993).

The Kelnase beds were named after the village on Prangli Island. In the Prangli section, they are represented by clayey silts with the pollen spectra characterized by an increasing quantity of Betula nana (40-80%) and herbs (tundra species). Gramineae and Cyperaceae are common. Selaginella selaginoides, Lycopodium alpinum and Artemisia arctica are present. A cryophilous and hydrophilous vegetation refers to the approaching glacial advance (Kajak et al. 1976, Liivrand 1991).

The Valgjärve beds, named after the lake in southern Estonia, are represented by grey till in northern and purplish-grey till and related aqueoglacial deposits in southern Estonia. The purplish-grey till was proposed for a specific stratigraphical unit by Orviku (1939) and described lithologically by Orviku (1958a) and Raukas (1963a, 1978). In the Kitse borehole No. 19 near Lake Valgjärv at a depth of 4.2-31.1 m, the till of the Valgjärve bed covers the organogenous deposits of the Prangli (Rõngu) Formation (Kajak 1995).

The Savala beds named after the village in northeastern Estonia belong to the M i d d l e  J ä r v a  S u b f o r m a t i o n (Kajak et al. 1976). The type section (borehole 7854, depth 25.8-30.2 m) is situated in the Savala ancient valley about 120 km east of Tallinn. It is mainly filled with grey-coloured varved clays. The pollen and spore composition of the intermorainic layer suggests dry periglacial conditions (Liivrand 1985, 1991). The Savala interstadial warming was not accompanied by any substantial development of forests.

The Võrtsjärve beds, named after Lake Võrtsjärv, are represented mainly by tills of different colour of the last glaciation and aqueoglacial deposits above and beneath the till. In several places some till layers with thin intermorainic interstadial or interphasial sediments occur (Orviku 1939, Raukas 1963a). Tills of the last glaciation on the Cambrian blue clays, sand- and siltstones in the fore-klint area are bluish-grey, mostly clayey and contain mainly clasts from Finland and the bottom of the Gulf of Finland. On the crystalline basement, the till is brown or reddish-brown. Stony tills on the Ordovician and Silurian bedrock are enriched with the local carbonaceous material (Photo 29). The constituent clasts are mainly angular. Tills on the Devonian sand- and siltstones are reddish-brown. The rather well-rounded local carbonaceous and erratic crystalline material occurs in various ratios in the cobble and pebble fractions and are under the influence of the Devonian bedrock, comparatively rich in sand and silt fractions (Orviku 1958a, Raukas 1978). In the stratotype area - the basin of Lake Võrtsjärv, both grey carbonaceous (Valma) and reddish-brown (Tamme) tills are widespread.