Geological History of the Dry Valleys, Antarctica, Based on the Stable Isotope Studies

Abstract

In 1973, DVDP 4 drilling was performed to obtain unconsolidated sediments of Lake Vanda, McMurdo Oasis. The cored sediments were found to contain layered salt concretions composed of gypsum, thenardite and calcite. On the basis of stable isotope compositions, δ^C, δ^O and δ^S, on the water and salts, it was concluded that the lake and the Wright Valley were once a fijord containing sea water and isolated from the ocean by glaciation. Micropaleontological studies for the cored sediments were also performed, indicating the existence of marine fossil fragments, marine sponge microsclere and marine centric diatom, only below the 1st gravel laver. This supports the above conclusions. In the 1975-1976 field survey season, layered mirabilite (or gypsum), ice and marine sediment, which were found under moraines at the height of 60 to 150 m above sea level near the coast of McMurdo Sound, have been studied on their occurrences and analyzed isotopically. These sulfate minerals and ice were found to be of marine in origin according to their isotopic compositions. This fact suggests that the sea water level largely fluctuated in geologic time and reached possibly 150 m higher than the present, and the present Wright Valley and Taylor Valley were under ocean water in the past.