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.