The period from the mid-Cretaceous (mid-Albian) to the mid-early Eocene (approximately 105 Ma to 55 Ma) was one of the warmest times in the late Phanerozoic. The average global temperature was probably about 6°C higher than that of today (Barron, 1983), allowing polar regions to be free of permanent ice. Temperatures were high enough to allow forests and vertebrates to live near both poles, particularly during the peak of warmth in the early Eocene. In contrast to the mid-Jurassic to early Cretaceous there is no evidence for seasonal ice (as ice-rafted deposits) in high latitudes from the Cenomanian to Maastrichtian, although there may have been seasonal ice present during the Palaeocene in northern high latitudes.

The mid-Cretaceous was a time of globally high sea levels and extensive areas of shallow shelf seas, favouring moderate climates and increased evaporation and precipitation (Arthur, Dean and Schlanger,1985).The oceans are believed to have been more stratified than at present, with little vertical mixing and the deposition of large quantities of organic-rich sediments in anoxic bottom waters. In particular, restricted circulation occurred in the developing Atlantic oceans, although by the latter part of the Cretaceous more open circulation was established and the deposition of black shales diminished. Sea levels reached their Mesozoic-Cenozoic peak in the late Cretaceous and then gradually dropped (Haq et al., 1987). During the latest Cretaceous the seas withdrew, exposing larger continental areas and leading to the establishment of more seasonal, continental climates (Hays and Pittman, 1973).

However, refined palaeotemperature data and reinterpretation of the thermal tolerances of fossil plants indicates that there were distinct warmer and cooler phases within the warm trend, particularly highlighted at high palaeolatitudes.