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A new model of anoxic facies and petroleum source-bed formation is based on the sapropel control of deciphered in the eastern Mediterranean. During the Late Jurassic, the Cretaceous, and other warm periods, formation of black marine sediments occurred near emerged lands, in semi-enclosed deep basins (South Atlantic); shallow basins on carbonate platforms (Saudi Arabia); and the open Equatorial Pacific. The globally warm climates, even at high latitudes, were very rainy. The tropics had a monsoon and a dry season. The small hemispheric temperature gradient weakened the atmospheric circulation, particularly the Hadley cell. Very weak tradewinds annihilated most of the coastal upwelling. Ocean surface currents were sluggish and bottom waters were warm, saline, and hadly circulating. The and drainage resulted in the accumulation of large deltas (Niger, Barreirinhas), but the sediment yield of rivers varied widely, as they do today. The key event for marine stagnation was the spreading on the sea surface of the huge river plumes which accumulated a low-salinity surface layer undisturbed by the weak winds, a process very common today off the tropical river mouths. The strong vertical salinity gradient (2 to 4^pmil) stratified the upper ocean and interrupted the (thermo) haline convection, so that the bottom waters, isolated in the basins or hardly circulating in the open ocean, became stagnant and oxygen-depleted. Sediments can therefore become organic-rich source beds whatever their lithology. Ocean productivity in the plume was greatly enhanced when rivers drained volcan c areas or swamps.

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