From Mens, K., & Pirrus, E. (1997):

The Voronka Formation was established by Mens and Pirrus (1971). Earlier, this part of the sequence was treated as two lower units of the post-Laminarites Sandstone or as the lower and middle parts of the Lomonossov Formation (Mardla et al. 1968). The type section of the formation is an outcrop on the lower reaches of the Voronka River, Russia (Mens & Pirrus 1971). Beyond the stratotype area, the formation is of subsurface occurrence being known in eastern and northern Estonia and in eastern Latvia. The Meriküla drill core in the interval of 90–109 m serves as a hypostratotype for the Voronka Formation (Mens & Pirrus 1980). The formation occurs between the overlying Lontova Formation and the weathering crust of the underlying Kotlin Formation (Mens & Pirrus 1969, 1970). In Estonia, the thickness of the formation ranges from 10 to 40 m. The Voronka Formation consists of variable siliciclastic rocks and represents a single upwards coarsening cycle from argillaceous rocks to well-sorted sandstones. The lower boundary of the formation is drawn on the basis of the change in colour. Based on lithological evidence, the formation is divided into the Sirgala and Kannuka members.