Neogene paleoenvironmental and geological history of the Transantarctic Mountain coastline and Victoria Land Basin: Initial results of ANDRILL’s Southern McMurdo Sound Project AND-2A drillcore

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Harwood, David۱; Florindo, Fabio۲; Levy, Richard۱; SMS, Science Team۳
Holding Date 08 October 2008

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. The quality of this drillcore is excellent, with more than 98% recovery through the cored interval. One objective of the SMS Project was to recover a history of ice-proximal paleoenvironmental variation during the middle Miocene, which has long been held as a fundamental step in development of the Cenozoic cryosphere. The AND-2A drillcore recovered several distinct stratigraphic intervals separated by disconformities: (a) a lower Miocene interval (1138.54 up to c. 800 mbsf) of an expanded section through an interval previously recovered during the Cape Roberts Project; (b) a 600 meter-thick middle Miocene interval (800 to 223 mbsf), which includes an expanded section through two middle Miocene climatic optima, is truncated by a disconformity that spans approx. 7 m.y.; and (c) an upper Miocene to Recent interval (223 to 0.0 mbsf) that is thinner but correlative to parts of the Late Neogene section recovered by ANDRILL’s McMurdo Ice Shelf Project in drillcore AND-1B. Shallow marine deposits dominate the lower SMS section until c.1.5 Ma when the basin deepened rapidly in response to volcanic loading by Mt Erebus. Early and middle Miocene strata record repeating lithological changes that reflect variation in sea-level, glacial proximity, and climate fluctuations on the shallow marine coast of the Transantarctic Mountains during the interval between c. 20 and 14.5 Ma. Sediments deposited close to or beneath grounded glaciers (likely flowing from East Antarctica) alternate with fine-grained marine sediments, providing clear evidence for cycles of ice advance, followed by substantial retreat during climate transitions to warmer conditions. Fossils preserved in these strata suggest non-polar climate conditions similar to southern Patagonia and 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 associated in-situ stress measurements for the Antarctic Plate, and further developed core visualization and data management technology. An excellent chronostratigraphy for the AND-2A drillcore, developing from combined biostratigraphy, magnetostratigraphy and radiometric dating of common tephra and volcanic materials, will provide age control for the drillhole and the network of seismic lines in the western Ross Sea. These results are vital to SCAR’s ACE program (www.ace.scar.org) whose objectives are 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.