A recent revision of a rich ammonite fauna from the Upper Cenomanian-Lower Turonian succession of central and eastern Tinrhert (Saharan Algeria) has shown that it contains six distinct biostratigraphical units. In addition, work on echinoids and bivalves has brought out the nature of the environments and the marked trends in the evolution of the benthic faunas. The limestones corresponding to the beginning of the great transgression of the Late Cenomanian (units 1 and 2), ascribed to the Zone of Calycoceras naviculare, are rich in ammonites and contain a diverse and abundant benthos. Units 3 and 4, which represent the highest part of the Cenomanian, are still rich in cephalopods but benthic forms are scarce or even very scarce; the same is true of unit 5 and the lower part of unit 6, both dated as Early Turonian. In the upper part of unit 6 the benthic fauna becomes locally abundant and diverse again. The environmental features inferred from the palaeontological content can be compared with the depositional conditions of the contemporary organic-rich succession of Eastern Maghreb. In central Tunisia the organic-rich beds of the Bahloul Member are the same age as chalky limestones in central Sahara, still rich in a planktonic fauna but with hardly any benthos. Therefore, on the Saharan Platform there was a weaker reflection of the palaeoceanographical processes that produced organic-rich sediments in basinal areas, corresponding to Oceanic Anoxic Event 2, but the marine environment was not so strongly disturbed that anoxic facies were formed. (C) 1999 Academic Press.