These results suggest that ice sheet-ocean feedbacks may have played a role in the origin of the middle Miocene transition. 15.5 Ma under strongly fluctuating sea surface temperatures until large ice sheets with massive ice shelves periodically became grounded on the shelf by ca. A transition to glacially dominated facies associations indicates that ice expansion took place at ca. In the AND-2A core, the middle Miocene climatic optimum (15-17 Ma) as recognized in proxy records, is characterized by facies indicating ice sheet and sea ice minima with a larger biogenic component. Based on the distribution of these facies motifs in the core it can be concluded that the middle Miocene Antarctic ice sheets were dynamic and accompanied by major base level changes. Motif 2 includes a wider variety of facies and is more consistent with a dynamic ice-sheet with facies characteristic of open marine to iceberg-influenced environments. Motif 1 is diamictite- dominated and represents glacially dominated environments, including subglacial environments, with only brief intervals of ice-free coasts. Although there is significant variability in the character and vertical arrangement of facies, two stacking patterns or motifs can be recognized. Sixty sequences were identified, each bounded by sharp-based conglomerates or diamictites. Here we present a facies model and an analysis of the sequence stratigraphy of AND-2A and discuss its implications for the interpretation of eustasy and ice volume proxies across the middle Miocene transition.

In 2007, ANDRILL drilled a 1138.54 m-deep hole (AND-2A) in southern McMurdo Sound into early Miocene to Pleistocene strata, including an expanded middle Miocene section.

Ms visual basic powerpacks