Time constraints on hydrocarbon migration and caprock formation recorded by calcite spar in a Carboniferous-Permian carbonate-evaporite succession, Finnmark Platform, Barents Sea

A late Carboniferous to early Permian carbonate and evaporite succession from the Finnmark Platform (southern Barents Sea) contains nodules of anhydrite partially to fully replaced by calcite spar and native sulfur genetically linked to hydrocarbon migration and/ or oxidation, analogous to processes observed in salt diapir caprocks in the Gulf of Mexico. In situ U-Pb dating of this calcite spar therefore has the potential to directly date hydrocarbon migration and provide further insight into the geochemical and temperature conditions during this event when coupled with traditional stable and clumped isotope ratios (delta C-13, delta O-18, and Delta 47). Results indicate calcite formed ca. 50-15 Ma, postdating host-rock deposition by 250-285 m.y. Strongly negative delta C-13 values in the calcite spar (mean = -15 parts per thousand) are consistent with a major contribution of carbon from hydrocarbons, and.47 paleothermometry indicates a mean precipitation temperature of 46 +/- 11 degrees C. These geochemical results are consistent with the local burial history and suggest protracted hydrocarbon migration and/or oxidation and caprock formation spanning similar to 35 m.y.

Automated summary

A Carboniferous to early Permian carbonate and evaporite succession from the Finnmark Platform in the southern Barents Sea contains nodules of anhydrite replaced by calcite spar and native sulfur, which are genetically connected to hydrocarbon migration and/or oxidation. In situ U-Pb dating of calcite spar can provide insights into the timing of hydrocarbon migration and the geochemical and temperature conditions during this event.