Growth rings in Cretacous and Tertiary wood from Antarctica and their palaeoclimatic implications
Although the Antarctic Peninsula now has a glacial climate, during the Cretaceous and early Tertiary it was sufficiently warm for forests to thrive, even at palaeolatitudes of 59°-62° S. The forests grew on an emergent volcanic arc and the wood was subsequently buried in fluvial and basinal sediments on the margins of the back-arc basin. The forests were composed mainly of podocarp and araucarian conifers. By the late Cretaceous, angiosperm trees were also present, particularly Nothofagus, forming the characteristic forest association of the southern hemisphere today. The growth rings in the fossil wood are wide and extremely uniform, indicating that the environment was very favourable for tree growth. By comparison with living forest trees with similar growth characteristics, a warm to cool-temperate climate is proposed for the Antarctic Peninsula in the Cretaceous and early Tertiary. Features of fossil floral assemblages and sedimentary rocks are also indicative of this type of climate. An increase in the level of atmospheric carbon dioxide is considered the most likely cause of the warm polar climate at this stage.