Graptolite reflectance and thermal maturity of Lower and Middle Ordovician shales from Scania, Sweden

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Abstract
Reflectance data from three bore cores in Scania, southern Sweden, are characteristic of moderately aromatic carbon species. The variation in graptolite reflectance is minimal, suggesting similar levels of thermal maturation. Measurements from graptolites associated with pyrite or carbonate are unreliable for maturation assessment. The graptolites display low anisotropy and have not been directly affected by the heat from numerous Permocar-boniferous dikes in Scania. The reflectance of the graptolites has been correlated with conodont alteration index and also indirectly with vitrinite reflectance indicating a thermal maturation level generally associated with the onset of dry gas generation. Dispersed bitumen in the shales probably migrated from sediments of lower thermal maturity.