CENOZOIC GLACIATION IN THE SOUTHERN HEMISPHERE

Abstract

With the end of glaciation in Gondwana in early Permian time, a prolonged interval began when the Earth was without ice sheets, though not necessarily free of mountain glaciers. Not until sometime during the Tertiary Era did ice sheets build up once more, first in Antarctica and later in the Northern Hemisphere. The fundamental cause of the cooling that led to the formation of the Antarctic Ice Sheet and, eventually, to major glaciation in lower latitudes is generally held to have been the increasing thermal isolation of Antarctica as Australia, and later South America, separated from it, allowing zonal oceanic circulation to develop. Rifting between Australia and Antarctica began between 1 10 and 90 m.y. ago (Cande & Mutter 1982), but not until much later, probably sometime between 30 and 25 m.y. ago, had it progressed far enough for deep circulation to begin as the South Tasman Rise cleared north Victoria Land (Kennett et a1 1974, Kennett 1977, Weissel et aI 1977). However, Antarctica did not reach its present high level of thermal isolation until South America had separated from it, enabling the Antarctic Circumpolar Current to become established (Savin et aI 1975). According to Barker & Burrell (1977, 1982), coherent spreading between the Antarctic Peninsula and Tierra del Fuego started about 29 m.y. ago, and deep circulation began 23.5 ± 2.5 m.y. ago, thereafter increasing in volume. The initial ice fields and ice caps that later expanded to become the