Major middle Miocene climate change and the extinction of tundra communities: Evidence from the Transantarctic Mountains

We present a glacial record from the western Olympus Range, East Antarctica, that documents a permanent shift in the thermal regime of local glaciers, from wet to cold based, between 14.11 and 13.94 million years ago (Ma). The record includes classic wet-based tills interbedded with fossil-rich glaciolacustrine deposits overlain by a series of cold-based drifts. Chronologic control comes from Ar/Ar analyses of six in-situ volcanic ash deposits. The shift from wetto cold-based glaciation reflects a drop in mean annual temperature of 20 to 30 ̊C and is shown to precede one or more major episodes of ice-sheet expansion across the region sometime between 13.62 and 12.44 Ma. Major implications are 1) that atmospheric cooling preceded, and thus may have triggered, maximum overriding of the polar East Antarctic Ice Sheet and 2) that complex terrestrial communities became extinct in this sector of the Transantarctic Mountains at ~14 Ma.