Tuesday, November 29, 2005

What was the Cretaceous like?

I think of the cretaceous period as a time of luxuriant abundance. Tropical rain forest probably covered at least 10% of the land mass, and that land mass had been significant reduced. Many continental areas where covered by shallow seas (at least in the early cretaceous). Australia was almost half covered by such shallow seas, covering the Great Artesian Basin, the Murray Basin, Ecula Basin and Canning Basin. It is also clear that sea levels fell dramtically in the late cretaceous.

The climate was certainly hotter (there were no permanent polar ice caps) and wetter (higher humidity and possibly regular rain) but the climate may have been more benign than today. Without a strong temperature and pressure gradient (from the equator to the poles) to drive currents in the oceans and winds in the atmosphere. Weathering of the surface rocks was deep and in the few places we see that surface preserved the soils show hydromorphic (waterlogged) structure and are commonly laterites and latsols (tropical soil types). Plants where abundant but in the early cretaceous there where no flowers. Still there here massive forests with diverse flora. The angiosperms (flowering plants) evolved and spread quickly in the late cretaceous help by the increase range of insects species and particularly bees.

Ref: The Paleogeographic map is from "The Geological Evolution of Australian and New Zealand" Brown D.A; Campbel K.S.W & Crook K.A.W, Perggamon Press

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