By the E/O boundary times, there is no doubt that ice was present on Antarctica. In the Ross Sea region, drill cores show evidence of relatively uniform marine sedimentation through the latest part of the Eocene and into the Oligocene but sediments include exotic clasts indicative of iceberg rafting. There does not appear to be a major environmental shift at this time but more of an intensification of cooling. In the Prydz Bay region, tidewater glaciers were present in the Early Oligocene, with ice reaching the continental shelf edge. In the oceans, the oxygen isotope record and other geochemical indicators signal a strong cooling at the boundary, the Oi-1 event, which has been interpreted as a time of major build-up of ice.
Even though climates were cold, vegetation was able to persist but by this time the higher diversity and warmth-loving plants of the Early and Middle Eocene forests had disappeared, to be replaced by vegetation that was dominated by several species of the southern beech, Nothofagus. Along with mosses, a few ferns and some podocarp conifers, southern beech trees probably grew as shrubby vegetation in the most hospitable areas.
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