Effect of thermal maturity on remobilization of molybdenum in black shales

摘要: Abstract Molybdenum (Mo) concentrations in sedimentary records have been widely used as a method to assess paleo-redox conditions prevailing the ancient oceans. However, potential effects of post-depositional processes, such thermal maturity and burial diagenesis, on Mo organic-rich shales not addressed, compromising its use redox proxy. This study investigates distribution speciation at various maturities Upper Ordovician Utica Shale from southern Quebec, Canada. Samples display ranging peak oil window ( VRo ∼ 1 % ) dry gas zone 2 ). While our data show significant correlation between total organic carbon (TOC) R = 0.40 , n 28 P 0.0003 lower maturity, this gradually deteriorates with increasing maturity. Intervals within thermally overmature section that contain elevated levels (20–81 ppm) petrographic sulfur isotopic evidence thermochemical sulfate reduction (TSR) along formation recrystallized pyrite. X-ray Absorption Fine Structure spectroscopy (XAFS) was determine samples intervals contents (>30 ppm). Our results presence two species: molybdenite Mo(IV)S 39 ± 5 Mo(VI)-Organic Matter 61 new suggests higher maturities, TSR causes coupled oxidation matter (OM). process is associated H S generation pyrite recrystallization. turn leads remobilization co-precipitation TSR-derived carbonates porous intervals. could lead alteration initial signature affected intervals, hence challenging proxy black shales.