More about Ordovician microfossil diversity patterns in the Rapla section, Northern Estonia

Diversity dynamics of acritarchs and chitinozoans was studied in the Rapla borehole section which embraces the Ordovician from the upper Arenig to the topmost Ashgill. The number of taxa per stratigraphic unit, the rate and total rate of appearing and disappearing taxa per unit or per 1 Ma, and diversity changes at the unit boundaries were analysed. Both groups demonstrate an energetic radiation–origination period in the Arenig–Llanvirn, a remarkable extinction event in the late Caradoc (top of the Keila Stage), and a mass extinction in the terminal Ordovician (Pirgu–Porkuni stages). Other diversity changes seem to be local and ecologically controlled. The general pattern of microfossil diversity is similar to that established by Sepkoski (Ordovician Odyssey, 1995) for some invertebrates.