Limited Pliocene Glacier Extent and Surface Uplift in Middle Taylor Valley, Antarctica

ABSTRACT

Limited surface uplift, glacial extent, and climatic change since mid-Pliocene time are inferred from surficial deposits in middle Taylor Valley, Antarctica (77°30'-77°50'S., 160°0'-163°40'E.). ⁴⁰Ar/³⁹Ar isotopie dates of whole-rock basalts constrain 14 subaerial volcanic eruptions between 3.89 and 1.50 Ma. The isotopic ages, subaerial nature, and present positions of these volcanic outcrops together are used to limit surface uplift to less than ≈ 300 m since 2.57 Ma. On the north wall of Taylor Valley, glacial drifts at Rhone Platform are intercalated with isotopically dated volcanic rocks and record at least four Pliocene-Pleistocene expansions of Taylor Glacier (>3.47 Ma; 2.97 Ma-2.71 Ma; <2.71 Ma; <1.50 Ma). The most extensive expansion reached 1082 m elevation, and occurred between 2.97 Ma and 2.71 Ma, whereas the other three were only slightly less extensive. Specific dates of reduced alpine glacier and Taylor Glacier extent (1.50, 2.20, 2.55, 2.71, 2.97, 3.52, and 3.74 Ma) come from the ages of subaerially erupted volcanic deposits that are now in contact with alpine glaciers. The implication of these data is that there has not been a significant change in the magnitude or character of glacial activity since mid-Pliocene time. All glacial deposits in middle Taylor Valley contain clasts with ventifaction and desert varnish, suggesting that desert conditions existed prior to 3.47 Ma. An in-situ layer of volcanic lapilli and bombs dated to 2.97 Ma rests on an intact desert pavement at 1075 m elevation on Rhone platform on the north wall of Taylor Valley.