Initial Results of Andrill's Southern McMurdo Sound Project Drillcore and-2A: Early Miocene to Recent Geological History of the Victoria Land Basin, Antarctica

Southern McMurdo Sound Project (SMS) of the ANDRILL Program (www.andrill.org), one of the larger IPY-endorsed programs, completed the AND-2A drillhole (77°45.488 S; 165°16.613 E) from a floating sea-ice platform (~8.5 meters thick), over ~380 meters of water, reaching a total depth of 1138.54 mbsf with an excellent recovery (>98%).One objective of the SMS Project was to recover a history of ice-proximal paleoenvironmental variation during the middle Miocene, a crucial period for the development of the Cenozoic cryosphere.

The AND-2A drillcore recovered several distinct stratigraphic intervals separated by disconformities: (a) an expanded section of lower Miocene (c. 350 m-thick) an interval previously recovered during the Cape Roberts Project; (b) a 600 meter-thick middle Miocene interval (800 to 223 mbsf) with an expanded section through two middle Miocene climatic optima truncated by a ~ 7 m.y disconformity; and (c) a thinner upper Miocene to Recent interval (223 to 0.0 mbsf) correlative to parts of the ANDRILL's McMurdo Ice Shelf Project drillcore AND-1B. Early and middle Miocene strata record repeating lithological changes where sediments deposited close to or beneath grounded glaciers alternate with fine-grained marine sediments, indicating cycles of ice advance and retreat. Fossils preserved in these strata suggest non-polar climate conditions resembling southwestern New Zealand today, influenced by high sediment discharge from river run-off, and high coastal turbidity.

The SMS Project achieved a nearly continuous downhole logging program, completed a hydrofracture experiment with in-situ stress measurements for the Antarctic Plate, and further developed core visualization and data management technology.

These results are vital to the ACE program (www.ace.scar.org) objectives to integrate geological and paleoclimatic data into climate and ice sheet models to constrain estimates of Cenozoic ice volume variability, and terrestrial and marine paleotemperature