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This Article Figures Only Full Text Full Text (PDF) All Versions of this Article: B26540.1v1 121/11-12/1537    most recent Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by McKay, R. Articles by Wilch, T. GeoRef GeoRef Citation

The stratigraphic signature of the late Cenozoic Antarctic Ice Sheets in the Ross Embayment

Robert McKay^1,, Greg Browne², Lionel Carter¹, Ellen Cowan³, Gavin Dunbar¹, Lawrence Krissek⁴, Tim Naish^1,2, Ross Powell⁵, Josh Reed⁶, Franco Talarico⁷ and Thomas Wilch⁸

¹ Antarctic Research Centre, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand
² GNS Science, P.O. Box 30368, Lower Hutt, New Zealand
³ Department of Geology, Appalachian State University, Boone, North Carolina 28608-2067, USA
⁴ School of Earth Sciences and Byrd Polar Research Center, Ohio State University, Columbus, Ohio 43210, USA
⁵ Department of Geology and Environmental Geosciences, Northern Illinois University, DeKalb, Illinois 60115-2854, USA
⁶ ANDRILL Science Management Office,126 Bessey Hall, University of Nebraska-Lincoln, P.O. Box 88085, Lincoln, Nebraska 68588-0341, USA
⁷ Università di Siena, Dipartimento di Scienze delle Terra, I-53100 Siena, Italy
⁸ Department of Geology, Albion College, Albion, Michigan 49224, USA

Correspondence: E-mail: robert.mckay{at}vuw.ac.nz.

A 1284.87-m-long sediment core (AND-1B) from beneath the McMurdo sector of the Ross Ice Shelf provides the most complete single section record to date of fluctuations of the Antarctic Ice Sheets over the last 13 Ma. The core contains a succession of subglacial, glacimarine, and marine sediments that comprise ~58 depositional sequences of orbital-scale duration. These cycles are constrained by a chronology based on biostratigraphic, magnetostratigraphic, and ⁴⁰Ar/³⁹Ar isotopic ages. Each sequence represents a record of a grounded ice-sheet advance and retreat cycle over the AND-1B drill site, and all sediments represent subglacial or marine deposystems with no subaerial exposure surfaces or terrestrial deposits. On the basis of characteristic facies within these sequences, and through comparison with sedimentation in modern glacial environments from various climatic and glacial settings, we identify three facies associations or sequence "motifs" that are linked to major changes in ice-sheet volume, glacial thermal regime, and climate. Motif 1 is documented in the late Pleistocene and in the late Middle Miocene intervals of AND-1B, and it is dominated by diamictite of subglacial origin overlain by thin mudstones interpreted as ice-shelf deposits. Motif 1 sequences lack evidence of subglacial melt-water and represent glaciation under cold, "polar"-type conditions. Motif 2 sequences were deposited during the Pliocene and early Pleistocene section of AND-1B and are characterized by subglacial diamictite overlain by a relatively thin proglacial-marine succession of mudstone-rich facies deposited during glacial retreat. Glacial minima are represented by diatom-bearing mudstone, and diatomite. Motif 2 represents glacial retreat and advance under a "subpolar" to "polar" style of glaciation that was warmer than present, but that had limited amounts of subglacial meltwater. Motif 3 consists of subglacial diamictite that grades upward into a 5- to 10-m-thick proglacial retreat succession of stratified diamictite, graded conglomerate and sandstone, graded sandstone, and/or rhythmically stratified mudstone. Thick mudstone intervals, rather than diatomite-dominated deposition during glacial minima, suggest increased input of meltwater from nearby terrestrial sources during glacial minima. Motif 3 represents Late Miocene "subpolar"-style glaciation with significant volumes of glacially derived meltwater.