Upper Llandovery to middle Wenlock (Silurian) lithostratigraphy and chitinozoan biostratigraphy in southwestern Estonia and northermost Latvia

The lithostratigraphy and chitinozoan biostratigraphy of the Adavere, Jaani, and Jaagarahu regional stages (upper Llandovery to middle Wenlock) in the Ikla (Estonia) and Staicelc (Latvia) drill cores were studied. Most of the upper Aeronian to lower Homerian local chitinozoan biozones are represented in these cores, except Interzone III, Angochitina longicollis, Conochitina proboscifera, and Margachitina margaritana biozones, partly corresponding to barren red beds of the Velise Formation, partly to a stratigraphical gap at the Llandovery-Wenlock transition. The presence of Stricklandia laevis shows that the Rumba Formation of the Adavere Stage belongs to the Telychian. The succeeding, Velise Formation has a reduced thickness and is represented only by its lower portion. Three stratigraphical gaps were established at the boundaries of the regional stages. The hiatuses at the junctions of the Raikküla-Adavere and Adavere-Jaani stages have a considerable areal extent and stratigraphical range. Probably, they reflect global glacio-eustatic falls of sea level at the end of the Aeronian and Telychian corresponding to the glaciations in South America. A gap at the base of the Jaagarahu Stage was recognized only in the Ikla core and has local significance