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, CO2Antarctic Geospatial Information Center, University of Minnesota,

Minneapolis, MN

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.

ANT scape

Time intervals for paleotopographic reconstructionFirst Priority:

1.~34 Ma• Landscape that supported first continental ice sheet when global

temperatures dropped from ~8 to ~4°C above present

2.~4 Ma• Pliocene warm period when global temperatures were ~3°C warmer

3.~50 Ma• Eocene warm peak (as distinct from the PETM at 55 Ma)• Warmest part of Greenhouse Earth (10-15°C warmer than present)• Will help address the question of formation of ABW in a Greenhouse

world

Time intervals for paleotopographic reconstructionSecond Priority:

4.14 Ma • Mid Miocene climate transition

5.~70 Ma • Antarctic margins were established once Gondwana breakup was

complete• The Late Cretaceous was a time of cool climate

6.~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

34 Ma restoration (Wilson and Luyendyk, GRL, 2009)

Image from Studinger and Barrett, 2009, Nature Geoscience

Factors accounted for:1.Loading from growth of ice sheets2.Subsidence from thermal contraction as a result of prior tectonic extension3.Erosion and sediment deposition4.Horizontal tectonic motion since 34 Ma

BEDMAP1_plus

WAIS initiation models / high topog

Pollard and DeConto, 2003

MBL Subaerial Volcano Ages

High summits and alpine areas absent at 34 Ma onset of continental Glaciation

17 Ma or younger (Mt Petras and Reynolds excepted)

LeMasurier and Rocchi, 2005

Glacial IncisionJamieson 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.

Red line --lithospheric boundary, inferred. Origin: intracontinental transform active in Cretaceous time.

Takahe, 3460m

Sidley, 4181 m

Hampton13.7 – 8.5 Ma

Perkins, 1178m c. 1.4 Ma

Siple, 3110 m

Petras29-25 Ma

Berlin, 3478m 2.5 Ma – 0 yr

Crary Mtns

Siddoway et al., 2005; Siddoway 2008; McFadden et al. 2009 in revision

Miocene Volcanoes and glacier streams

BEDMAP1_plus

WARS

Mt Takahe

Ford Ranges

~21 Ma Reconstruction

WARS

BEDMAP1_plus

Analyzed cross-sectional profiles of bedrock topography (BEDMAP1_plus) on a 40 km grid

BEDMAP1_plus

Analyzed cross-sectional profiles of bedrock topography (BEDMAP1_plus) on a 40 km grid

AssumptionsVolcanism - 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

Methods, assumptions, and reasoning - Volcanoes

Methods, Assumptions, and Reasoning - Incised glacial valleys

Methods, Assumptions, and Reasoning - Sediment volumes

For more in-depth treatment, see Wilson and Luyendyk, GRL, September 2009

Alpine glacier troughs in Executive Committee Range

Flexural Moat around Executive Committee Range

Conclusions

• ANTscape’s 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

Methods, Assumptions, and Reasoning

BEDMAP1_plus

Mt Takahe

WARS

Ford Ranges

~21 Ma Reconstruction

WARS