Date of this Version
The lower portion of the CIROS-1 core (McMurdo Sound, Antarctica) has been cited as evidence for Late Eocene continental glaciation on Antarctica. A reassessment of this age determination is warranted in the face of mounting evidence from multiple proxies that continental glaciation was initiated by rapid ice-growth during the earliest Oligocene. Examination of calcareous nannofossil assemblages from this section confirmed very low fossil abundance, low species richness, and the presence of reworked taxa. A minimum of 37% of the total species richness in the section comprises reworked forms, including Late Cretaceous and latest Paleocene to Middle Eocene species. Quantitative analysis suggests a further 20-33% of the species were part of the reworked component. Given the very low abundance, sporadic occurrence, and predominance of demonstrably reworked species in the CIROS-1 section, coupled with the well-documented reworking in nearby Cape Robert Project Oligocene strata, the biostratigraphic integrity of the remaining species is clearly suspect. At best, a latest Eocene to Early Oligocene age assignment is justified. The large uncertainty in the age determination indicates that the CIROS-1 section cannot be used as evidence of a pre-Oligocene initiation of Antarctic continental glaciation.