The terrestrial environment during Upper Cretaceous and tertiary times

Abstract

The Address reviews the geography, climate, soils and vegetation of the land areas of the North Atlantic region from Upper Cretaceous to the threshold of Pleistocene times. It is suggested that during the Upper Cretaceous, in a climate of tropical heat and humidity, the lands were covered by thick soils of lateritic type. Erosion was very slow, and the rivers carried little erosional debris; the silica and bases derived from the chemical weathering of the rocks were carried into the Chalk Sea to form flint and chalk. The vegetation was rather uniform over the whole of the northern hemisphere, and there were no ocean barriers to hinder the dispersion of plants, some of which showed adaptations to the hot humid climate. Tropical conditions continued into Tertiary times. During the Palaeogene there was a tropical rain forest in the area surrounding the London-Hampshire basin, and a tropical swamp on the North German plain. The vegetation of the Arctic was of a warm temperate type. The fossil floras of Mull and Antrim are regarded as early Tertiary in age. The spread of tropical rain forest over large areas of the world during the Upper Cretaceous and Lower Tertiary times is related to the appearance of suitable habitats on low-lying lands exposed by marine regressions and on the shores of the new continental rifts, and is suggested as a possible cause of the extinction of the dinosaurs. The Arcto-Tertiary flora of conifers and deciduous trees continued to cover the higher, drier lands. The inter-basaltic red boles of Antrim are interpreted as tropical soils of ferallite type, which later became laterised as the result of water-logging. The fossil leaf floras of Mull and Antrim are related to the climatic conditions indicated by the soils. During the Miocene the climate became less tropical and the tropical rain forest disappeared. In the Pliocene the vegetation indicates warm, humid conditions.