Silurian acanthodian succession of the Lužni-4 borehole (Latvia)

Acanthodians of the Luzni-4 borehole core include about 50 species and other dermal element forms distributed in the late Ludlow to the topmost Pridoli. Eleven acanthodian associations are obtained classified as the intervals (=intervals of partial ranges) of index species. Ranges of taxa which characterize the local and regional stratigraphical units are given, and most valuable species are distinguished. The earliest occurence of Nostolepis gracilis in the Baltic region is reported from the late Ludlow, a lower stratigraphic level than previously recognized. Some taxa, such as Nostolepis latvica sp. nov., N. alifera sp. nov., N. cf. linleyensis, Rohonilepis breviornatus, Arenaceacanthus arcuatacanalis, Fecundosquama basiglobosa, Poracanthodes marssae sp. nov., have biozonal utility, and Nostolepis linleyensis, Gomphonchus mediocostatus, Monospina erecta, Paracanthodes spp., are significant for wide interregional correlations. The short-ranging topmost Pridolian acanthodian associations of the Luzni-4 lack some taxa characteristic of the deepest water Jura Formation as compared to southwestern Lithuania, perhaps indicating a shortened geological profile in this basin part.