Graptolite biozone correlation charts

Charts are presented showing the correlation of graptolite biozonations for the Lower Ordovician to Lower Devonian, i.e. for the entire stratigraphical range of the planktonic graptoloid graptolites. Regions chosen are those for which the most detailed biostratigraphical studies have been undertaken. For Baltica, average graptolite zone (chron) duration appears to vary from c. 300 000 years (Ludlow Epoch) to 2.4 Ma (Lochkovian Epoch).