A sparsely encrusted hardground with abundant Trypanites borings from the Llandovery of the Velise River, western Estonia (Baltica)

The Päärdu hardground from the Telychian (Rumba Formation) of western Estonia is sparsely encrusted (0.4% of the studied surface) by possible tabulate corals, sheet-like bryozoans and discoidal echinoderm holdfasts. Both the upper and cryptic sides of the hardground are intensely bioeroded by Trypanites borings. The taxonomic composition of the Päärdu hardground association is rather different from the characteristic Silurian association in being dominated by tabulate corals, while bryozoans and echinoderms played a minor role in the association. The Päärdu hardground is more sparsely encrusted than common for the Late Ordovician and Silurian hardgrounds, but this may be a characteristic feature of the hardgrounds of Baltica. The Päärdu hardground is important among the Silurian hardgrounds because it has unusually low encrustation combined with high bioerosion.