Phosphorites

Abstract

Phosphorite deposits are confined to upwelling at continental margins, where a high flux of organic material supplies phosphorus to the sea floor. In this environment anaerobic sulfur bacteria concentrate and release phosphorus, which then precipitates as francolite. The formation of a phosphorite deposit requires a long-term delicate balance of mud sedimentation and episodic reworking, and consequently phosphorite deposits only accumulate at continental margins with a very slow average sedimentation rate.