Miocene-Pliocene-Pleistocene paleoclimate and glacial history of the western Dry Valleys region, Antarctica

Abstract

A case is made for the stability of the polar East Antarctic Ice Sheet since middle-Miocene time from landscape development and surficial sediments in the western Dry Valleys region, southern Victoria Land. The alternate hypothesis that calls for repeated Miocene and Pliocene growth and decay of wet-based ice sheets across East Antarctica requires atmospheric temperatures 20"C above present values and late Pliocene ice-sheet overriding of the Transantarctic Mountains. The geomorphological and sedimentological results suggest that these conditions were not met in the western Dry Valleys. Rather, mean annual atmospheric temperatures during the last 13.6 Ma were at most only 3° to SoC above present values; ice-sheet overriding occurred in middle Miocene time (> 13.6 Ma); and Pliocene glacier expansion was limited. These conclusions are based on field studies in the western Asgard Range and in the Quartermain Mountains. The chronology comes from ⁴⁰Ar/³⁹Ar laser fusion analyses on individual volcanic crystals and glass shards removed from in-situ volcanic ashes that occur in stratigraphic association with unconsolidated diamictons in the western Dry Valleys region. The combined geomorphological and sedimentological evidence indicates that slope evolution in the western Dry Valleys was severely restricted since at least the middle Miocene. The implication is that most of the landscape is relict and that it reflects ancient erosion under semi-arid climate conditions prior to middle-Miocene time.