Phosphatic chalks accumulated in water depths of between 70 m and a few hundred metres in oxic, current-swept areas of an open epicontinental sea of normal salinity. High surface productivity, moderate organic-carbon fluxes, reduced sedimentation rates and high rates of sediment mixing led to the precipitation of phosphate within hardground surfaces and carbonate grains. Bacterial decomposition of organic matter raised phosphate contents in pore waters and promoted the geochemical conditions necessary for phosphate precipitation. Phosphate precipitates, now transformed to carbonate fluorapatite, include um-sized ovoid bodies and massive coatings interpreted to be of microbial origin. Phosphatization was a rapid process occurring under mixed aerobic/anaerobic redox conditions in the upper decimetre of the sediment column, close to the sediment-water interface. Phosphatization took place predominantly within the confines of the cuvettes, where phosphate grains became concentrated by current winnowing and transport. Phosphatic chalk sedimentation occurred on the NE and northern margins of the Anglo-Paris Basin following regressive events that enabled bottom currents to erode the cuvettes and maintain productivity and the other sedimentary conditions necessary for phosphate accumulation.