The Mid-Cretaceous epicontinental sea covered the central part of the Russian Craton (RC). It was differentiated into a series of syn-sedimentary highs and lows. The highs are called phosphate platforms. They are confined to inherited tectonic uplifts where Precambrian basement is very shallowly buried and earlier Mesozoic and Palaeozoic sediments are thin or wedged out altogether. Cenomanian sediments on the highs represent condensed sequences and contain abundant hiatuses. They are crowned by an extensive phosphorite pavement, 30-50 cm thick, which is a multi-layered phosphorite hardground, built of phosphorite nodules firmly cemented by a phosphate matrix. The nodules consist of phosphatized radiolarians, diatoms and hexactinellid sponges. Analyses show no carbonate in excess of what is substituted for PO 3 - 4 in the francolite structure, nor is the enclosing sediment carbonate-bearing. Thus the Cenomanian phosphorites of the RC differ from those of the Anglo-Paris basin. During the Cenomanian, sea-level rose little because eustatic rise was compensated for by continued epirogenic uplift of the area. This delicate balance was abruptly broken by a major rise of sea-level which happened around the Cenomanian-Turonian boundary (CTB) and led to the drowning of the phosphate platforms and deposition of the chalk.