Subglacial Landform Analysis and Reconstruction of Miocene Paleotopography of Marie Byrd Land

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Subglacial Landform Analysis and Reconstruction
of Miocene Paleotopography of Marie Byrd Land

• Perry Spector1,2, Christine Siddoway1, and Paul
  Morin2
•  
• 1Dept Geology, Colorado College, Colorado
  Springs, CO
• 2Antarctic Geospatial Information Center,
  University of Minnesota, Minneapolis, MN

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ANTscape

• International group of Antarctic researchers and
  climate scientists
• ACE subcommittee on Antarctic Paleotopographic
  Maps
• 3 yr mission Create a series of series of
  paleotopographic maps from Cretaceous to Present
  which
• Show change in bedrock elevations, landforms,
  and geotectonic configuration of Antarctica over
  the past 100 Ma.
• Visualizations of past landscapes
• Provide a geographical base for diverse
  paleo-environmental data
• Cretaceous through Recent climate variations
• Biological evolution and biodiversity
• Glacial cycles and growth of continental ice
  sheets.

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Time intervals for paleotopographic reconstruction

• First Priority
• 34 Ma
• Landscape that supported first continental ice
  sheet when global temperatures dropped from 8 to
  4C above present
• 4 Ma
• Pliocene warm period when global temperatures
  were 3C warmer
• 50 Ma
• Eocene warm peak (as distinct from the PETM at 55
  Ma)
• Warmest part of Greenhouse Earth (10-15C warmer
  than present)
• Will help address the question of formation of
  ABW in a Greenhouse world

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Time intervals for paleotopographic reconstruction

• Second Priority
• 14 Ma
• Mid Miocene climate transition
• 70 Ma
• Antarctic margins were established once Gondwana
  breakup was complete
• The Late Cretaceous was a time of cool climate
• 92 Ma
• Continental separation had occurred on all but
  the West Antarctic margin
• Intracontinental extension underway in the WARS
• Early Cretaceous was a time of warm climate
  (Miller et al, 2005)
• 20 m sea level drop observed in the
  oceanographic record is attributed to glaciation

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34 Ma restoration (Wilson and Luyendyk, GRL, 2009)
Image from Studinger and Barrett, 2009, Nature
Geoscience

• Factors accounted for
• Loading from growth of ice sheets
• Subsidence from thermal contraction as a result
  of prior tectonic extension
• Erosion and sediment deposition
• Horizontal tectonic motion since 34 Ma

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BEDMAP1_plus
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WAIS initiation models / high topog
Pollard and DeConto, 2003
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MBL Subaerial Volcano Ages
17 Ma or younger (Mt Petras and Reynolds excepted)
High summits and alpine areas absent at 34 Ma
onset of continental Glaciation
LeMasurier and Rocchi, 2005
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Glacial Incision
Jamieson and Sugden, 2008 -Following mid-Miocene
climate transition, Antarctica entered an arid
period when extensive areas of the ice sheets
became cold-based. Warm-based glacial erosion
became focused within preexisting drainages at
low elevation, leading to development of deeply
incised outlet glacier troughs.
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Miocene Volcanoes and glacier streams
Crary Mtns
Petras 29-25 Ma
Berlin, 3478m 2.5 Ma 0 yr
Red line --lithospheric boundary, inferred.
Origin intracontinental transform active in
Cretaceous time.
Siddoway et al., 2005 Siddoway 2008 McFadden et
al. 2009 in revision
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BEDMAP1_plus
Mt Takahe
WARS
Ford Ranges
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21 Ma Reconstruction
WARS
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BEDMAP1_plus
Analyzed cross-sectional profiles of bedrock
topography (BEDMAP1_plus) on a 40 km grid
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BEDMAP1_plus
Analyzed cross-sectional profiles of bedrock
topography (BEDMAP1_plus) on a 40 km grid
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Assumptions

• Volcanism - Interpret the majority of eastern MBL
  subglacial vertical relief to be a result of
  volcanism
• Close proximity to subaerial volcanoes
• Topographically concentric morphology
• Comparison with findings of numerous subglacial
  volcanoes from CWA geophysical surveys.
• Glacial Incision Certain deep,
  structurally-controlled troughs have been further
  deepened by glacial incision
• Sedimentation - Deep, structural basins have been
  locations of deposition

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Methods, assumptions, and reasoning - Volcanoes
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Methods, Assumptions, and Reasoning - Incised
glacial valleys
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Methods, Assumptions, and Reasoning - Sediment
volumes
For more in-depth treatment, see Wilson and
Luyendyk, GRL, September 2009
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Alpine glacier troughs in Executive Committee
Range
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Flexural Moat around Executive Committee Range
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Conclusions

• ANTscapes effort to create a series of
  paleotopographic maps of Antarctica over the past
  100 Ma
• MBL volcanoes are 17 Ma to present (Petras and
  Reynolds excepted) and thus were not present to
  serve as high elevation sites for ice cap
  nucleation during early history of WAIS.
• Alpine glacier troughs on 14 Ma and younger
  volcanoes of Executive Committee Range
• Wet-based erosive features formed at high
  elevations after the mid-Miocene climate
  transition (change to hyper arid climate and
  onset of cold-based mode of Antarctic glaciation
  (Jamieson and Sugden, 2008)) is a possible
  indication of elevated basal thermal conditions
  in the vicinity of the volcanoes.
• Volcanic moat on north and south margins of
  Executive Committee Range
• Potentially show the need of accounting for
  volcanic rock in addition to ice in isostatic
  corrections of WANT

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Methods, Assumptions, and Reasoning
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BEDMAP1_plus
Mt Takahe
WARS
Ford Ranges
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21 Ma Reconstruction
WARS