Granulometry, geochemistry, amino acids, radiocarbon ages and paleomagnetics of samples from Heidemann Valley

A Pliocene (2.6-3.5 Ma) age is determined from glacial sediments studied in a 20m long, 4 m deep trench excavated in Heidemann Valley, Vestfold Hills, East Antarctica. The age determination is based on a combined study of amino acid racemization, diatoms, foraminifera, and magnetic polarity, and supports earlier estimates of the age of the sedimentary section; all are beyond 14C range. Four till units are recognized and documented, and 16 subunits are identified. All are ascribed to deposition during a Late Pliocene glaciation that was probably the last time the entire Vestfold Hills was covered by an enlarged East Antarctic Ice Sheet (EAIS). Evidence for other more recent glacial events of the 'Vestfold Glaciation' may have been due to lateral expansion of the Sorsdal Glacier and limited expansion of the icesheet margin during the Last Glacial Maximum rather than a major expansion of the EAIS. The deposit appears to correlate with a marine deposition event recorded in Ocean Drilling Program Site 1166 in Prydz Bay, possibly with the Bardin Bluffs Formation of the Prince Charles Mountains and with part of the time represented in the ANDRILL AND-1B core in the Ross Sea.本研究对东南极洲维斯特福尔德丘陵（Vestfold Hills）海德曼谷（Heidemann Valley）开挖的20米长、4米深探沟中的冰碛沉积物开展研究，确定其沉积年代为上新世（2.6~3.5 Ma）。该年代测定基于氨基酸外消旋作用、硅藻、有孔虫与磁极性的综合分析，验证了此前对该沉积剖面年代的估算结果；所有测年结果均超出碳十四（¹⁴C）测年范围。研究识别并记录了4套冰碛单元，同时划分出16个次级单元。上述所有单元均形成于晚上新世冰期，该冰期可能是维斯特福尔德丘陵全域被扩张后的东南极冰盖（East Antarctic Ice Sheet, EAIS）覆盖的最后一次冰川事件。所谓‘维斯特福尔德冰期’（Vestfold Glaciation）中其他较年轻冰期的证据，实则可能源于末次盛冰期（Last Glacial Maximum）期间索斯达尔冰川（Sorsdal Glacier）的侧向扩张以及冰盖边缘的有限扩张，而非东南极冰盖的大规模扩张。该沉积物序列可与普里兹湾大洋钻探计划（Ocean Drilling Program, ODP）1166站位记录的海相沉积事件相对比，或可对应查尔斯王子山脉的巴丁断崖组（Bardin Bluffs Formation），以及罗斯海地区南极钻探计划（ANDRILL）AND-1B岩芯所记录的部分时间段。