Identification of the O-bentonite in the deep shelf sections with implication on stratigraphy and lithofacies, East Baltic Silurian

Pyroclastic sanidine composition is used for correlation of the Osmundsberg bentonite (O-bentonite) bed from Estonia to Latvia. Chemical changes during conversion of volcanic ash to authigenic silicates in shallow and deep shelf sediments differ, leading to the formation of kaolinite-rich bentonite in deep shelf and feldspar-rich bentonite in shallow shelf environments. The Rumba Formation in Estonia is proved to be of Lower Telychian age. Firmly based correlation between shallow and deep shelf sediments allows tracing of facies variations that occurred during environmental changes in the Late Llandovery times.