Stratigraphy and facies differences of the Middle Darriwilian Isotopic Carbon Excursion (MDICE) in Baltoscandia

The Middle Darriwilian Isotopic Carbon Excursion (MDICE) is a global isotopic event described in sections from different palaeocontinents. Here we present new stable carbon isotopic data from carbonates of ten sections in different parts of the Baltoscandian Palaeobasin (Estonia, Latvia, Lithuania, Sweden. NW Russia). The definition of the MDICE as a chemostratigraphic unit is discussed, as well as the subdivision of its peak into two distinct peaks. The MDICE is one of the longest carbon isotopic events in the Palaeozoic. It was preceded by the L-chondritic cosmic dust flow event, which may have been responsible for cooling through the Darriwilian and the initiation of the Great Ordovician Biodiversification Event. High-resolution chemostratigraphic analyses show that the time interval between these environmental events and the base of the MDICE is up to one million years. Due to the long duration of the MDICE the modelling of this excursion should address more complex scenarios than a simple response of the carbon cycle to rapid climatic perturbations.