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Abstract

The Cretaceous was a time of decreased freeboard, when large portions of all continents were flooded by shallow marine waters. Suggested causes for this decrease in freeboard are a decrease in the volume of the ocean basins caused by more rapid sea floor spreading rates during the Cretaceous (Kominz, 1984) and a thermal bulge in the Pacific during this time (Schlanger et al., 1981). Kominz (1984) has analysed the possible errors involved in attempting to determine the volume of the ridge crests during the Cretaceous, and came to the conclusion that sea level was 228 m higher than today 80 m.y. ago. This included an estimate for the amount of continental ice present today, which was assumed to he absent during the Cretaceous. Schlariger et al. (1981) estimated a sea level rise of 80 m 70 m.y. ago, by studying thermal subsidence of areas in the Pacific which were known to show very large volcanic activity between 110 and 70 m.y. ago. A recent compilation of the causes of sea level change, in which ridge crest volume, thermal subsidence, ice volume, thermal shrinking of the water column, increased sediment load today compared with the Cretaceous, and increased oceanic area due to continental collision following closure of Tethys were all considered, gave a sea level increase 80 m.y. ago of 278 in (Harrison, 1985).

Of particular interest to the readers of this volume are the sea level changes which produce the transgressive-regressive cycles seen in the sedimentary deposits of the Western

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