EAST ANTARCTIC NEOGENE FOSSIL MOLLUSCS - DISTRIBUTION, AMINO ACID GEOCHRONOLOGY AND CORRELATION

The recognition and age determination of Antarctic Neogene marine deposits has principally been based upon microfossil content and biostratigraphic correlation of key species. Neogene fossil mollusc assemblages, composed almost entirely of bivalves, are known from three coastal sites, Vestfold Hills, including the Marine Plain site, Larsemann Hills and Lützow-Holm Bay, and from one inland locality, the northern Prince Charles Mountains, in East Antarctica. Bivalve fossils generally tend to be fragmented and dispersed among medium to coarse-grained glacial marine sediments. Two localities among these sites, Vestfold Hills and Pagodroma Gorge in the Prince Charles Mountains, feature in situ preservation of fossil mollusks within finer grained, deeper water facies preserved in a stratigraphic context.

Amino acid geochronology has proven to be a very useful means of determining ages and correlation between these localities. Amino acid data suggests that multiple episodes of marine deposition are preserved along the East Antarctic continental margin. Analytical results indicate that the earliest preserved Neogene fossils are middle to late Miocene age from the Dragon’s Teeth Cliffs section in the Prince Charles Mountains. Shells preserved in Pagodroma Gorge suggest deposition of this deposit between 2.0 and 3.3 ma. In the Vestfold Hills, amino acid ratios suggest two episodes of Neogene deposition with Marine Plain deposited during the early Pliocene and Heidemann Valley shells having a middle to late Pliocene age. Shells recovered in Lutzow-Holm Bay are correlative with the younger Heidemann Valley episode. Depositional evidence suggests that the middle-late Pliocene shells may have been reworked by subsequent ice sheet expansion.

This Neogene fauna features low species diversity, only a dozen species have been recovered, and is dominated by infaunal species. Species composition in these fossil assemblages is a mixture of extant species and others that are presently extinct in Antarctica. Only one species, Hiatella sp., is common to all four localities, though it is presently extinct in Antarctic waters. Although the species found in East Antarctic Neogene mollusc faunas offer limited biostratigraphic utility, many specimens preserve valuable reservoirs of amino acids for geochronologic analysis.