Thermal evolution of the Ordovician in the western margin of the East-European Platform: CAl and Ro data

Values of colour alteration index of conodonts (CAI), based on collections from Ordovician strata of 40 boreholes, have been established for the area of the pre-Vendian Platform in northeastern Poland and adjacent southwestern areas of younger consolidation. Changes of the CAI are shown on maps. Six zones of similar CAI values are distinguished. Their presumed ranges beyond the boundaries of Poland are outlined basing on data from the adjacent countries. A spatial distribution of paleotemperatures was achieved in this way yielding new data which may serve to interpret the thermal history of the Early Palaeozoic deposits in the western slope of the East-European Platform. The changes of CAI are correlated with the results of vitrinite reflectance measurements (Ro) from selected profiles.