Chitinozoan biostratigraphy in the Haljala Regional Stage, Upper Ordovician: a high-resolution approach from NE Estonia

The distribution of chitinozoans in the Haljala Stage (Upper Ordovician, Sandbian) from Kerguta-565, Piilsi-729 and Vasknarva-639 drill cores in NE Estonia was examined from 128 closely spaced samples. The studied chitinozoan fauna was diverse – altogether 14 chitinozoan genera and 39 species were recorded. Based on chitinozoan ranges in the studied sections, 13 species were identified as biostratigraphically most valuable. The high-resolution sampling used in this study has allowed us to refine the stratigraphic usefulness and extent of distribution of several chitinozoan key species as well as elaborate internal biostratigraphy of the Haljala Stage.