Upper Wenlock to Lower Pridoli (Silurian) conodont biostratigrphy of Saaremaa, Estonia, and a correlation with Britain

The closely related conodonts Ozarkodina bohemica, O. snajdri and O. crispa form a clade that provides useful biostratigraphical indices through the upper Silurian. Collections from boreholes and surface outcrops on Saaremaa and from a borehole at Kolka, Latvia, contain new morphotypes of O. bohemica and O. crispa. A new subspecies, O. snajdri parasnajdri, is also distinguished, occurring above O. crispa in the Kuressaare and lowermost Kaugatuma stages. Evidence from conodonts and other fossils, primarly chitinozoans, ostracods and ichthyoliths, can be used to correlate the upper Silurian succession of Saaremaa with those of the Welsh Borderland and Gotland, although some problems remain to be solved. The microfossil distribution suggests that there may be a major break at the base of the Ludlow Bone Bed Member at Ludlow, equivalent to the Kuresaare Formation on Saaremaa.