The Cambrian–Ordovician Boundary beds at the Tônismägi section in Tallinn, North Estonia, are represented by siltstones and sandstones with interlayers of clay and kerogenous argillites. In this section, three conodont zones – Cordylodus proavus, C. intermedius and C. rotundatus-angulatus – were established. Graptolites of the Rhabdinopora flabelliforme group were found in the upper part of the C. proavus Zone. This section demonstrates that in suitable facies, species of Rhabdinopora may appear earlier than usually considered.

The Baltic Phosphate Basin contains a condensed sequence of late Upper Cambrian-early Ordovician sediments. These consist mainly of mature quartz sandstones with debris of phosphatic shells of inarticulate brachiopods, notably Schmidtites and Ungula. The sequence also contains Dictyonema shales and glauconitic sandstones. A large-scale exploration project completed recently has delineated several new promising areas, including the Rakvere deposit in northeastern Estonia where resources amount to as much as 700 Mt of P205 contained in easily beneficiated ores grading 10% P205.

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