Reconstruction of a grounded ice sheet in McMurdo Sound : evidence from Southern Black Island, Antarctica
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Conflicting reconstructions exist for Last Glacial Maximum (LGM) ice configurations in McMurdo Sound, yet climatic modelling studies such as the landmark CLIMAP11 investigation, are critically reliant on ice sheet reconstructions in this region. In more recent reconstructions, there is disagreement over grounding line position, ice flow directions, ice surface contours and chronology of ice sheet retreat. The most significant divergence occurs in the region surrounding southern Black Island, which in turn hosts a significant glacial and geological cover that has been little studied.
Fifteen days were spent mapping striated basement, geomorphic features, sediment/ erratic distribution and collecting samples on four diamict-covered, bedrock promontories at the southern end of Black Island. Petrographic, petrological and geochemical analyses were carried out on erratic and bedrock samples. Grain size analyses were undertaken to better characterise the diamict cover.
Two new units, Cape Beck Phonolite (Cbp) and Cold Bluffs Tephriphonolite (Cbt), belong to the Erebus volcanic lineage and are the most evolved units of the Black Island volcanic complex. An 40Ar/39Ar age range of 1.8–1.7 Ma was obtained from Cbp lava flows, providing a maximum age constraint for deposition of glacial material. Mapped geomorphic features are a product of both glacial erosion and periglacial weathering processes, with the latter predominant during recent times. Several newly defined glacial facies are defined by two drift units. Cape Beck Drift is not a correlative of the Ross Sea Drift (RSD), and is believed to be a more antiquated Quaternary deposit. Younger drift is considered to be the Last Glacial Maximum response to ice fluctuations in Southern McMurdo Sound (SMS).
Drift composition and distribution and glacial striae on Cbp indicate an ice sheet was grounded in SMS when the Cape Beck Drift was deposited. Granite erratics and glacially polished bedrock, proxies for ice elevation, mark the minimum height of the ice sheet at 590 m a.s.l., indicating that it completely overrtopped southern Black Island.
The glacial reconstruction presented in this study was constrained by the orientations of 150, previously unrecorded, glacial striae and the distribution of key erratics in the Cape Beck Drift, which support northerly trending ice flow of the main lobe of the SMS ice sheet. This flow direction is antipodal to those presented by the CLIMAP reconstruction and its derivatives.
The discrepancies between RSD reconstructions and the reconstruction of this study, highlight the need to re-assess the glacial deposits in the McMurdo Sound region that have been ascribed a LGM age, and are assumed to be related to most extensive configuration of the Antarctic Ice Sheet.
Fifteen days were spent mapping striated basement, geomorphic features, sediment/ erratic distribution and collecting samples on four diamict-covered, bedrock promontories at the southern end of Black Island. Petrographic, petrological and geochemical analyses were carried out on erratic and bedrock samples. Grain size analyses were undertaken to better characterise the diamict cover.
Two new units, Cape Beck Phonolite (Cbp) and Cold Bluffs Tephriphonolite (Cbt), belong to the Erebus volcanic lineage and are the most evolved units of the Black Island volcanic complex. An 40Ar/39Ar age range of 1.8–1.7 Ma was obtained from Cbp lava flows, providing a maximum age constraint for deposition of glacial material. Mapped geomorphic features are a product of both glacial erosion and periglacial weathering processes, with the latter predominant during recent times. Several newly defined glacial facies are defined by two drift units. Cape Beck Drift is not a correlative of the Ross Sea Drift (RSD), and is believed to be a more antiquated Quaternary deposit. Younger drift is considered to be the Last Glacial Maximum response to ice fluctuations in Southern McMurdo Sound (SMS).
Drift composition and distribution and glacial striae on Cbp indicate an ice sheet was grounded in SMS when the Cape Beck Drift was deposited. Granite erratics and glacially polished bedrock, proxies for ice elevation, mark the minimum height of the ice sheet at 590 m a.s.l., indicating that it completely overrtopped southern Black Island.
The glacial reconstruction presented in this study was constrained by the orientations of 150, previously unrecorded, glacial striae and the distribution of key erratics in the Cape Beck Drift, which support northerly trending ice flow of the main lobe of the SMS ice sheet. This flow direction is antipodal to those presented by the CLIMAP reconstruction and its derivatives.
The discrepancies between RSD reconstructions and the reconstruction of this study, highlight the need to re-assess the glacial deposits in the McMurdo Sound region that have been ascribed a LGM age, and are assumed to be related to most extensive configuration of the Antarctic Ice Sheet.
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xiv, 150 p. : ill., maps ; 30 cm. + 1 CD-ROM (4 3/4 in.) and 3 maps.
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2006Timms
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POLYGON ((166.504243443131173 -78.304870235822406,166.118671614482025 -78.307956731074682,166.11338772136034 -78.250217432958465,166.49553126832916 -78.247161801360178,166.504243443131173 -78.304870235822406))
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Timms, Carolyn Jean., “Reconstruction of a grounded ice sheet in McMurdo Sound : evidence from Southern Black Island, Antarctica ,” Otago Geology Theses, accessed June 8, 2026, https://theses.otagogeology.org.nz/items/show/476.