Neogene benthic foraminiferal assemblages and paleoenvironmental record for McMurdo Sound, Antarctica

Abstract

The Antarctic Geological Drilling (ANDRILL) program recovered a 1,138-m-long core, AND-2A, during the austral spring 2007–2008 from the Victoria Land Basin for the Southern McMurdo Sound (SMS) Project. The main objective of the SMS Project was to establish a Neogene (ca. 24–2.5 Ma) history recording ice volume changes from an ice-proximal site, in particular the environmental response of the Antarctic margin during the middle Miocene climate transition. This study focuses on the foraminifera taxa recovered from AND-2A, providing a paleoenvironmental analysis including paleobathymetry and ice-proximity estimates. Three assemblages, Cibicides-Cassidulinoides , Ammoelphidiella , and Ehrenbergina , as well as two subassemblages within the Ammoelphidiella assemblage, Globocassidulina and Nonionella , were identified in this study using cluster analysis. Calcareous eurytopic taxa dominate every assemblage and display similarities between Fresh Shelf Water assemblages and Ice Edge Biofacies that were previously defined in other studies focused in the Southern Ocean, as well as assemblages recovered from previous drilling projects in the Ross Sea region. Paleoenvironmental interpretations include an early Miocene record of fluctuating periods of glacial influence from ice-distal, abrupt cooling followed by a continued warming and transition into a more ice-proximal setting in the uppermost middle Miocene. The well-preserved middle Miocene record reflects more productive stable environmental conditions with significant freshwater input from outlet glaciers and rivers at the East Antarctic margin, and coincides with previously published palynomorph data indicating a short abrupt warming. Furthermore, the persistent appearance of the planktonic species Neogloboquadrina pachyderma and glacial/sea ice assemblages can be related to the onset of progressive cooling at the Antarctic margin, including periods of fluctuating sea ice extent or glacial proximity. Finally, the Pliocene record contains taxa similar to that of Fresh Shelf Water assemblages and Ice Edge Biofacies recovered in the Southern Ocean today. Paleobathymetric estimates range from inner shelf depths (∼50–150 m) in the early Miocene reaching periods of outer-shelf depths (∼400 m) in the uppermost early–middle Miocene and Pliocene.