Degree of Pyritization (DOP) and Indicator of Anoxicity (IA) in Jurassic sedimentary rocks from Bulgaria

The Degree of Pyritization (DOP) and the Indicator of Anoxicity (IA) were used as tools to assess the degree of redox conditions in Lower and Middle Jurassic strata from Bulgaria. Normally-oxygenated (with DOP values < 0.45 and IA values < 0.4), oxygen-restricted (0.45 < DOP < 0.7; 0.4 < IA < 0.5), and oxygen-depleted (DOP > 0.7 and IA > 0.5) bottom-water conditions were recognized on a selection of samples, mainly from the Ozirovo Formation (upper Pliensbachian–Toarcian), but also from the Etropole Formation (lower Bajocian). DOP and IA yielded the highest values (> 0.9 for DOP and > 0.5 for IA) from samples of the lower Toarcian Tenuicostatum and Falciferum ammonite zones, and thus, denoted declined oxygen levels and enrichment of reactive Fe at the sea floor. Beyond this stratigraphic level, both parameters indicated for prevailing normally-oxygenated to oxygen-restricted setting, with limitedly imposed environments beneath stratified water-column.