UPPER WENLOCK TO LOWER PRIDOLI (SILURIAN) CONODONT BIOSTRATIGRAPHY OFSAAREMAA, ESTONIA, AND A CORRELATION WITH BRITAIN

The closely related conodonts Ozarkodina bohemica, O. snajdri and O. c rispa form a clade that provides useful biostratigraphical indices thr ough the upper Silurian. Collections from boreholes and surface outcro ps on Saaremaa and from a borehole at Kolka, Latvia, contain new morph otypes of O. bohemica and O. crispa. A new subspecies, O. snajdri para snajdri, is also distinguished, occurring above O. crispa in the Kures saare and lowermost Kaugatuma stages. Evidence from conodonts and othe r fossils, primarily 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, equiv alent to the Kuressaare Formation on Saaremaa.