Stevns Klint

Diagenesis of Flint and Porcellanite in the Maastrichtian Chalk at Stevns Klint, Denmark

Flint nodules in the Maastrichtian chalk of Stevns Klint, Denmark, form through early diagenetic processes driven by microbial activity and low sedimentation rates. The study identifies four types of siliceous nodules—porcellanite, white flint, white flint with a dark core, and dark flint—composed primarily of microquartz, lutecite, chalcedony, megaquartz, and dolomite. Stable isotope analysis (δ18Osmow) indicates precipitation temperatures ranging from 15–17°C for microquartz and lutecite to up to 48°C for megaquartz, suggesting a transformation pathway from silica gel or opal-CT via dissolution-precipitation (Ostwald ripening). The research proposes that microbial decomposition of organic matter at the redox boundary below the seafloor initiated flint formation during periods of minimal sedimentation. This process implies that flint deposition reflects shallow-water conditions with high biosiliceous input and microbial activity, offering potential paleo-oceanographic insights for shallow carbonate systems.