Noncalcified dasyclad algae from the Vasalemma Formation, late Sandbian (Late Ordovician) of Estonia

The Vasalemma Formation, late Sandbian, Late Ordovician in Estonia contains a previously unknown flora of noncalcified dasyclad algae. The Vasalemma Formation is a locally restricted limestone unit, which is predominantly composed of an echinoderm grainstone. The formation, in its central areas, contains bryozoa- and echinoderm-rich reefs, and associated with these reefs, small patches of dolomitic lime-mudstone with an algal-Lagerstätte occur. The macroalgae are preserved as thin carbonaceous film associated with pyrite without any micro-structures evident. Three taxa could be distinguished: Chaetocladus vasalemmense Kröger, et Tinn spec. nov., Chaetocladus sp., Eocladus estoniense Kröger, et Tinn spec. nov. All three taxa have simple monopodial morphologies and delicate laterals. Remarkable is the occurrence of branched laterals in E. estoniense, which to our knowledge, is among the earliest occurrence of this morphotype. The Vasalemma algae flora can be compared with roughly contemporaneous occurrences in North America, which show similarities in depositional environments and associated fauna but differ in morphological and taxonomical diversity. •New Ordovician Algal-Lagerstätte is described.•Two new chaetocladine taxa are proposed.•Restricted marine depositional environment is inferred.•Algae are associated with lingulate brachiopods.