Cenomanian nodular phosphorites are widespread over vast areas of the Precambrian East European Platform (EEP). They are found in various parts of the Cenomanian forming thicker and richer beds close to the Cenomanian/Turonian boundary. They are encountered nearly unbiquitously, but are concentrated on synsedimentary highs in thin and condensed sequences with numerous hiatuses. All of the economic deposits are confined to the palaeohighs. Phosphorite pavements made of amalgamated, reworked and concentrated concretions are typical of the condensed sequences. More complete successions occur in the adjacent lows, where Upper Cenomanian sediments have been proved. Phosphorite in the lows are found as in-situ concretions either scattered irregularly or aligned in rows and spaced rather regularly. Calculations show that some 25 Gt of P2O5 was buried during the Cenomanian. A positive deltaC-13 anomaly was found to coincide with a thin layer of sandy to silty chalk, containing phosphatic intraclasts. The layer lies directly on the youngest and thickest pavement. The anomaly is believed to represent Oceanic Anoxic Event 2 (OAE-2) on the EEP. Consequently, (1) phosphorite pavement is most probably of Upper Cenomanian age, and (2) phosphogenesis is related to OAE-2. There is no black shale amidst the Upper Cenomanian on the EEP and sea-level variation during that time might be responsible for both the spatial and temporal differentiation of phosphorites and black shales. The former were deposited during transgressive phases, whereas the latter correspond to subsequent sea-level highstand. The extent of spatial differentiation might be preconditioned by the scale of difference between corresponding sea-levels. An upwelling scenario is hardly probable to explain the origin of the Cenomanian phosphorite of the EEP. A river-input mechanism is more probable, as it was advocated by Bushinsky.
