Long-term effect of the Kärdla crater (Hiiumaa, Estonia) on Late Ordovician carbonate sedimentation

Kärdla impact crater, 4km in diameter, was formed in the early Caradoc (Late Ordovician) in the Baltoscandian shelf sea, a sediment-starved temperate-water carbonate basin. The Upper Ordovician post-impact sediments that cover the Kärdla crater are 15–275m thick. The crater rimwall is composed of three separate basement rises that formed islands or shoals in the Late Ordovician shelf sea and influenced the sedimentation in the surrounding area. The rises provide the means to study the shallow-water sedimentary environments and sea-level history. This may be one of the few cases, where shore environments of the Baltoscandian Ordovician palaeobasin are preserved in the geological record. Lithofacies distribution was studied in the crater area from data of about 100 drillcores. Grain size distribution and composition of the non-carbonate material were analyzed in six core sections in order to reconstruct the history of crater erosion.