Early and Middle Miocene Antarctic Glacial History from the Sedimentary Facies Distribution in the AND-2A Drill Hole, Ross Sea, Antarctica

• Published in: Geological Society of America Bulletin
• Main Authors: Passchier, Sandra, Browne, G., Field, B., Fielding, Christopher R., Krissek, L. A., Panter, Kurt, Pekar, Stephen F.
• Format: Text
• Language: unknown
• Published: Montclair State University Digital Commons 2011
• Subjects: Antarctic; The Antarctic; Ross Sea; Antarc*; Antarctica; Ice Sheet; Iceberg*; Sea ice
• Online Access: https://digitalcommons.montclair.edu/earth-environ-studies-facpubs/252; https://doi.org/10.1130/B30334.1

In 2007, the Antarctic Geological Drilling Program (ANDRILL) drilled 1138.54 m of strata ̃10 km off the East Antarctic coast, includ ing an expanded early to middle Miocene succession not previously recovered from the Antarctic continental shelf. Here, we pre sent a facies model, distribution, and paleoclimatic interpretation for the AND-2A drill hole, which enable us, for the first time, to reconstruct periods of early and middle Miocene glacial advance and retreat and paleo environmental changes at an ice-proximal site. Three types of facies associations can be recognized that imply significantly different paleoclimatic interpretations. (1) A diamictite-dominated facies association represents glacially dominated depositional environments, including subglacial environments, with only brief intervals where ice-free coasts existed, and periods when the ice sheet was periodically larger than the modern ice sheet. (2) A stratified diamictite and mudstone facies association includes facies characteristic of open-marine to iceberg-influenced depositional environments and is more consistent with a very dynamic ice sheet, with a grounding line south of the modern position. (3) A mudstone-dominated facies association generally lacks diamictites and was produced in a glacially influenced hemipelagic depositional environment. Based on the distribution of these facies associations, we can conclude that the Antarctic ice sheets were dynamic, with grounding lines south of the modern location at ca. 20.1-19.6 Ma and ca. 19.3-18.7 Ma and during the Miocene climatic optimum, ca. 17.6-15.4 Ma, with ice-sheet and sea-ice minima at ca. 16.5-16.3 Ma and ca. 15.7-15.6 Ma. While glacial minima at ca. 20.1-19.6 Ma and ca. 19.3-18.7 Ma were characterized by temperate margins, an increased abundance of gravelly facies and diatomaceous siltstone and a lack of meltwater plume deposits suggest a cooler and drier climate with polythermal conditions for the Miocene climatic optimum (ca. 17.6-15.4 Ma). Several periods of major ice growth with ...