DEPOSITIONAL ENVIRONMENT, THERMAL MATURITY AND IRRADIATION EFFECTS ONPORPHYRIN DISTRIBUTION - ALUM SHALE, SWEDEN

The Swedish Alum Shale, which was deposited from Middle Cambrian to Lo wer Ordovician time in the shallow marine waters of the Lapetus Ocean, contains abundant uranium. The sedimentary organic matter associated with these shales has undergone irradiation, which has affected both t he insoluble and soluble portions. Rock extracts from the Alum Shale c ontain exclusively vanadyl porphyrins indicating deposition under a ma rine anoxic environment. The decrease in the concentration of porphyri ns with increasing uranium content indicates that irradiation has dest royed porphyrins. Comparison of the detailed vanadyl porphyrins distri bution does not show any preferential destruction of particular vanady l porphyrin, i.e., DPEP or ETIO, due to irradiation. Hence the porphyr in maturity parameter, which is based on the changes in the relative c oncentration of ETIO and DPEP porphyrins, can be used for estimating t he maturity of the Alum Shale regardless of its uranium concentration. This also suggests that the effect of irradiation on porphyrins is di fferent from that of heating.