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Kirjeldus

From: Mens, K., & Pirrus, E. (1997). Vendian. In Geology and mineral resources of Estonia (pp. 35–38). Estonian Academy Publishers. 

The Gdov Formation. Asatkin (1937) derived the name from the Gdov beds used as a division to denote the sandy strata between the “Laminarites” Clay and the crystalline basement in the northwestern part of the East-European Platform. The Gdov Formation is considered as the lower part of the Kotlin Stage accumulated during the initial phase of the Late Valdaian transgression over the northwesternmost part of the East-European Platform, including the present-day Estonia, Latvia, and the western part of the Leningrad Region.

In Estonia, the Gdov Formation rests immediately upon the crystalline basement and spreads in subsurface lying in the northern, eastern and central parts of the Republic. Its thickness ranges from 0.2 to 58.3 m. The Venevere drill core in the interval of 287–322.8 m has been selected as a hypostratotype for Estonia. The formation consists mostly of multicoloured sandstones of various grain size. The uppermost and, locally, also the lowermost part comprises a considerable quantity of reddish and purplish argillaceous rocks. The sandstones are represented by arkose and feldspatic varieties comprising besides quartz up to 50% of feldspars. Micas, both muscovite and green altered biotite, are occasionally found. The mineral composition of the clay fraction is rather stable throughout the formation, being characterised by illite-kaolinite suite (Pirrus 1970). On the basis of lithological features, the Gdov Formation is subdivided into three members, which, in ascending order, are: Oru, Moldova and Uusküla.