Spore–pollen evidence for early Oligocene high-latitude cool climatic episode in northern Canada

Abstract

Climatic cooling in the Eocene leading to markedly lower temperatures in the Oligocene has been documented in oxygen isotope studies in the North Pacific1,2, New Zealand3, South Pacific4 and North Sea5. These lower temperatures in the Oligocene correspond to palaeoclimatic interpretations of North American leaf floras6,7 which suggest a profound cooling occurring towards the end of the Eocene, indicated also in the southeastern United States from studies on mid-Tertiary spores and pollen8. Recently, Collinson et al.9 have shown palaeobotanically that in southern England cooling occurred gradually starting in the latest early Eocene leading to two major periods of floristic change before the end of the Eocene. Thick Tertiary sections in the subsurface Mackenzie Delta region, Northwest Territories10,11 provide well-preserved Palaeogene palynofloras12 discussed here which indicate a cooler climate in the Oligocene following warm-temperate conditions in the Eocene. This widespread early–middle Oligocene cool episode is thus represented in both high-latitude and lower-latitude floras and seems to have been of global extent, persisting until towards the end of the Oligocene, but its precise dating remains a problem. In northern Canada it is followed by an amelioration of the climate in the late Oligocene which persisted probably until the middle Miocene. The rate of cooling during the Eocene and Oligocene may have varied depending on locality, but once established the cooler Oligocene climate exerted a profound influence on biotic development.