Non-marine diatoms from late Wisconsin perched deltas in Taylor Valley, Antarctica

Abstract

Late Wisconsin perched deltas in Taylor Valley, Antarctica, and environs contain numerous, well-preserved diatoms characteristic of antarctic inland waters. Twenty-seven non-marine species and fragments of the marine species were encountered. Of the non-marine species, six ( Achnanthes taylorensis, Navicula airdevronsixii, Navicula deltaica Navicula papilio, Navicula quaternaria, and Nitzschia westii) are new. In various combinations, the 37 species form six floral assemblages. One assemblage is restricted to deltas in nearby Ferrar Valley, three are related to delta age or elevation within Taylor Valley, and one contains poorly preserved fragments of marine species. The significance of the sixth assemblage is not clear because it occurs in deltas of widely varying age, elevation, and geographic location. Many of the diatoms found in the deltas occur today in lakes that are characterized by highly variable ionic concentration and composition (from nearly fresh to super-saline). These saline lakes are not synonymous with a marine environment. For this reason, the species indicate non-marine rather than fresh-water or marine paleoenvironments. Glacial Lake Washburn, in which the Taylor Valley deltas were deposited, was non-marine. Occasional fragments of marine diatoms are attributed to reworking of older Ross Sea drift. The ice dam that blocked Lake Washburn in Taylor Valley between about 21 200 B.P. and about 8340 B.P. was apparently grounded, consistent with the contention that a former grounded ice sheet filled McMurdo Sound and the Ross Sea. The non-marine nature of the Taylor Valley deltas refutes the hypothesis (Miagkov et al., 1976) that sea level in the Ross Sea region was about 308 m higher than it is today at 17 000–21 200 B.P. We suggest that similar deltas in nearby Salmon Valley were deposited in small non-marine lakes dammed by ice-cored moraines deposited by the last Ross Sea glaciation. This interpretation is in contrast to the hypothesis (Miagkov et al., 1976) that the Salmon Valley deltas, which contain many of the same non-marine diatom species found in Taylor Valley deltas, formed in sea water along the ice-sheet edge during a general lowering of sea level caused by tectonism.