It has been proposed that the cause of the Cretaceous transgression may be found in the volume of ridge crest material. High spreading rates produce a greater volume of material, which displaces sea water and causes flooding of the continents. A direct corollary of this is that the average oceanic heat flow during these times of high sea level must be greater, since heat flow is closely connected to oceanic age and thus crustal elevation. Calculations show that the 85 m.y.b.p. the average oceanic heat flow was 1.35 times its present value. Variations of average oceanic heat flow must be taken into account in any model of mantle convection.