Early and middle miocene antarctic glacial history from the sedimentary facies distribution in the AND-2A drill hole, Ross sea, Antarctica

Sandra Passchier, G. Browne, B. Field, C. R. Fielding, L. A. Krissek, K. Panter, S. F. Pekar

Research output: Contribution to journalArticle

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Abstract

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 a grounding line traversing the drill site are recognized between ca. 20.2 and 17.6 Ma, and after ca. 15.4 Ma, with evidence of cold polar glaciers with ice shelves. The AND-2A core provides proximal evidence that during the middle Miocene climate transition, an ice sheet larger than the modern ice sheet was already present by ca. 14.7 Ma, ̃1 m.y. earlier than generally inferred from deep-sea oxygen isotope records. These findings highlight the importance of high-latitude ice-proximal records for the interpretation of far-field proxies across major climate transitions.

Original languageEnglish
Pages (from-to)2352-2365
Number of pages14
JournalBulletin of the Geological Society of America
Volume123
Issue number11-12
DOIs
StatePublished - 1 Nov 2011

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glacial history
ice sheet
Miocene
grounding line
depositional environment
ice
diamictite
Hypsithermal
mudstone
climate
subglacial environment
Antarctica
distribution
sea
iceberg
coast
ice shelf
siltstone
meltwater
oxygen isotope

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Passchier, Sandra ; Browne, G. ; Field, B. ; Fielding, C. R. ; Krissek, L. A. ; Panter, K. ; Pekar, S. F. / Early and middle miocene antarctic glacial history from the sedimentary facies distribution in the AND-2A drill hole, Ross sea, Antarctica. In: Bulletin of the Geological Society of America. 2011 ; Vol. 123, No. 11-12. pp. 2352-2365.
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Early and middle miocene antarctic glacial history from the sedimentary facies distribution in the AND-2A drill hole, Ross sea, Antarctica. / Passchier, Sandra; Browne, G.; Field, B.; Fielding, C. R.; Krissek, L. A.; Panter, K.; Pekar, S. F.

In: Bulletin of the Geological Society of America, Vol. 123, No. 11-12, 01.11.2011, p. 2352-2365.

Research output: Contribution to journalArticle

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AU - Passchier, Sandra

AU - Browne, G.

AU - Field, B.

AU - Fielding, C. R.

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