Mats Eriksson

A succession of 26 conodont zones and 63 successive subzones and conodont faunas have been identified in the exposed latest Landovery to latest Ludlow strata of Gotland, Sweden. All zones, and several of the subzones and faunas, have been identified elsewhere on Baltica as well as on other palaeocontinents, indicating that this zonation serves well as the standard zonation for calcareous successions. The average duration of the 24 Wenlock and Ludlow zones was 396+/-208 ka, using the latest radiometric timescale. However, most zones and subzones formed during the widely recognised Silurian oceanic events correspond to less time per unit - in the order of 30 to 100 ka - and most of those formed during intervening episodes correspond to a few 100 ka. The average duration of the 61 Wenlock and Ludlow zones, subzones, and faunas was only 156+/-82 ka, i.e., among the highest biostratigraphical resolution available for Phanerozoic epochs. On Gotland the combined known maximum thickness of the strata has increased to more than 750 m.