Conditions of forming and mineral features of Devonian terrigenous sediments in the Tsilma river basin in the Middle Timan

The problem of Rudyanka structure is considered. Its decoding, apart from the palynological analysis, used mineral features of the Devonian sedimentary rocks. It is established that the quantity of grains of plagioclase with polysynthetic twinnings greatly varies depending on the age of deposits. In terminal Middle Devonian sandstones (Ustchirkka formation) they are either absent or found in single grains (up to 6 pieces per a microsection). In the Upper Devonian rocks the quantity of plagioclase clasts are estimated in dozens and hundreds per a microsection. At local scale, the quantity of plagioclase grains may be considered as a mineral indicator of a continental sediments age.