Chitinozoans of the Margachitina margaritana Biozone and the Llandovery-Wenlock boundary in West Estonian drill cores

The succession of chitinozoan taxa in the uppermost Llandovery and lowermost Wenlock of the Viki, Ohesaare, Kaugatuma, and Ruhnu drill core sections is described and correlated with the global stratotype section of the basal Wenlock in Hughley Brook, Shropshire, England. The most important biomarkers for the identification of the Llandovery-Wenlock boundary in Estonian sections are the disappearance levels of Ramochitina nestorae, Conochitina acuminata, C. cf. flamma, and Angochitina longicollis. In the West Estonian cores this boundary corresponds to a level in the middle or upper part of the Margachitina margaritana Biozone. In the Viki and Ohesaare cores it coincides with the bentonite layers above the accepted boundary between the Adavere and Jaani regional stages and correlates with a level in the middle of the murchisoni graptolite Biozone. Three new species, Belonechitina oeselensis, Ancyrochitina mullinsi, and Eisenackitina inanulifera, are described.