SILURIAN BIOEVENT STUDIES A PART OF THE IGCP PROJECT 216 “GLOBAL BIOLOGICAL EVENTS IN EARTH HISTORY”

exciting old idea of catastrophes (= events) in Earth history, (b) the idea is promising good practical applications for detailed correlation of sections, and (c) high level activity of the project. Speaking about catastrophes, one usually means (mass) extinction events, but innovation, radiation, etc. events are not less interesting. The Silurian was preceded by the well-known late Ordovician glaciation-triggered extinction (O/S Boundary Event) and followed by several events of different scale and origin within the Devonian (a major one, the so-called Kellwasser Event seems to be very instructive for Silurian students as a typical anoxic layer oscillation event with a complex of other factors; Walliser, 1986). In the Silurian A.J. Boucot (1990) Ilisted the following levels at which relatively minor bioevents occurred: Co—Cs boundary (late Llandovery) in the early Wenlock, the late Wenlock, the late Ludlow, and the Silurian-Devonian boundary. Until now these events have gained little attention, but the top Wenlock, the (undgreni event and the following leintwardinensis event were thoroughly described from the aspect of graptolite diversity changes by T. Koren (1987). The first level was earlier known also as the dubius-nassa Interregnum (Jaeger, 1976), which might be called also the nassa-ludensis crisis (Great Crisis H. Jaeger, oral comm.). Ranking of events is rather arbitrary, but exact definition of a level where something happens is important. Otherwise we cannot distinguish whether there was a “big” event or a series of minor ones. For example, when the late Wenlock or Wenlock-Ludlow Boundary or lundgreni event