Light element distributions (N, B, Li) in Baltic Basin bentonites record organic sources

The Cambrian Alum shale, a regional hydrocarbon source rock, was studied as a potential source of B and Li, as more than 50% of its B and Li was associated with organic matter. With increasing thermal maturity, illite δ11B decreased from 0‰ to −13‰, while δ7Li increased from −20‰ to −5‰. These opposing trends are similar to those observed in the K-bentonites. This suggests that organic sources of N, B and Li dominate fluids in bentonites from the southwestern Baltic Basin, whereas basement derived fluids dominate in the northeastern Baltic Basin. These trace elements record paleofluid changes during illite crystal growth and can identify pathways of chemically distinct oil and gas related fluids.