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Kirjeldus

From Raukas & Kajak (1997):

The Ugandi Formation, called after an ancient South-Estonian and North-Latvian area, where those deposits are most widespread, is correlated with the Žeiminiai Formation in Lithuania, Kurzeme in Latvia, Middle Russian in Russia and Saale in Western Europe. In some places Middle Ugandi interstadial beds have been described. Borehole 6 on Prangli Island (depth 75.5-123.0 m) and borehole 268 at Valguta (13.1-35.0 m) have been established as the unit and boundary stratotypes for northern and southern Estonia, respectively (Raukas et al. 1993).

The till of the L o w e r  U g a n d i  S u b f o r m a t i o n, which is correlated with the Dniepr till in Russia and the Žemaitia till in Lithuania, is reddish-brown both in northern (Prangli, Naissaar, Suurpea) and southern Estonia (Mägiste, Lanksaare, Sudiste) and up to 50 m thick (Mägiste). The till is compact and occurs in uplands mainly in sheltered position or rests in ancient valleys. The clast lithology (high content of Vyborg rapakivi in eastern Estonia) indicates that the Lower Ugandi till was deposited by the southward flowing ice (Raukas 1978). Clasts in northern Estonia are almost completely fragments of crystalline rocks, whereas in southern Estonia their composition reflects both the local provenance (up to 10% of local Devonian sand- and siltstones) and the influence of the outcropping carbonaceous rocks on the way of the moving ice (50-60% carbonaceous clasts). Of all Estonian tills, it has the highest content of sandy fraction. In clay fraction illite (50-70%) prevails, but also the content of kaolinite is rather high (20-45%).

M i d d l e  U g a n d i sands, silts, loams and sandy loams often contain rebedded pollen and their stratigraphic position is not clear (Liivrand 1991).

U p p e r  U g a n d i till is massive to slightly stratified, reddish-brown in the fore-klint area (Prangli, Juminda) and grey in northern (Sõrve, Saadjärv) and southern (Rõngu, Suur-Munamägi) Estonia. The till unit is up to 70 m thick (Suur-Munamägi) and often cemented with carbonates. According to its composition (absence of Vyborg rapakivi and quartz-porphyries from the Island of Suursaari), the till entrained by southeastward flowing ice. Practically all the clasts in the fore-klint area originate in the crystalline basement, but in other areas carbonate rocks prevail (65-80%). In southern Estonia, this till has the highest content of silt particles and the lowest content of Devonian material. Illite (65-80%) prevails and the content of kaolinite (10-20%) is low in the clay fraction.

The aqueoglacial deposits of the Lower (Puiestee 60 m) and Upper (Vääna-Jõesuu 60 m) Ugandi subformations are rather thick and variable in composition (Raukas 1978).