Rapid transformation of biogenic silica to authigenic clay: Mechanisms and geochemical constraints

Authigenic clay formation during early diagenesis of marine sediments, termed "reverse weathering," is an important process for regulating ocean pH, seawater chemistry, and atmospheric CO₂ over geologic time scales. Although the importance of reverse weathering has been increasingly recognized, the rates and mechanisms remain poorly constrained. This study investigated the mechanisms, kinetics, and mineral products derived from diatom biogenic silica. We show the formation of Fe(II)-bearing smectite and mica in 40 days, the most rapid process and first specific mineral phases reported to date. Unraveling the kinetics and mechanisms of authigenic clay formation suggests that reverse weathering is far more dynamic and responsive to changes in ocean chemistry than previously envisioned, with a potential to impact marine alkalinity cycling on a shorter timescale.