. "Summary and Highlights of the 10th International Symposium on Antarctic Earth Sciences--T. J. Wilson, R. E. Bell, P. Fitzgerald, S. B. Mukasa, R. D. Powell, and C. Finn ." Antarctica: A Keystone in a Changing World. Washington, DC: The National Academies Press, 2008.
of northern Victoria Land is correlative with the western Lachlan fold belt of eastern Australia, and the Lachlan orogen rocks form in an extensional basin. The Cambrian rocks (Ross orogen correlatives) in New Zealand and Marie Byrd Land simply represent parts of a continental rift margin on the outboard side of the Lachlan fold belt (Bradshaw, 2007).
New models have been proposed for the origin of the West Antarctic rift system and the associated Transantarctic Mountains. Considerable debate at the symposium centered on the plateau hypothesis, in which the West Antarctic rift system and Transantarctic Mountains are thought to have been previously a high-topography plateau with thicker than normal crust. The proposed West Antarctic plateau is inferred to have collapsed in the Cretaceous during extension between East and West Antarctica. The Transantarctic Mountains are, in this hypothesis, the remnant western edge of the plateau modified by rift-flank uplift and glacial erosion. The first numerical model of the concept shows that plateau collapse could generate a remnant edge, depending on initial conditions (Bialas et al., 2007). The geological and thermochronologic evidence for the West Antarctic plateau formation and collapse, along with the tectonic implications, are discussed by Fitzgerald et al. (2007). Evidence for a drainage reversal in the Byrd Glacier region supports the presence of the West Antarctic plateau in the Mesozoic (Huerta, 2007). A synthesis of research from the exposed portion of the rift in Marie Byrd Land demonstrates that elevated crustal temperatures were attained by 140 Ma, causing voluminous melting, with lateral migration into wrench structures (Siddoway, 2008, this volume). Presence of melt aided the rapid evolution of the Cretaceous rift.
Other new geodynamic models of Antarctica were advanced at the symposium, emphasizing the significance of Antarctica to studies of global geodynamics (see Figure 1). Sutherland (2008, this volume) presents a model for extension in the West Antarctic rift system, a model that fits well with global plate model circuits and the geology of New Zealand. An elegant “double-saloon-door seafloor spreading” model explains the breakup of Gondwana, magnetic anomalies in the Weddell Sea region, along with the rotation and translation of the Falkland Islands block and the Ellsworth-Whitmore Mountains crustal block (Martin, 2007).
LIFE IN ANTARCTICA: THE TERRESTRIAL VIEW
A definitive incremental change in our understanding of the evolution of life on Antarctic land emerged at the symposium, from the rich and diverse terrestrial presentations. Evidence of a vibrant world is preserved in nonglacial and glacial sedimentary deposits that rest on top of the tectonic basement structures.
Insights into Gondwana ecosystem dynamics are being gleaned from tracks of animals in Devonian deserts (Bradshaw and Harmsen, 2007); the climate records in Permian, Triassic, and Jurassic floras (Bomfleur et al., 2007; Miller and Isbell, 2007; Ryberg and Taylor, 2007); and the Triassic and Jurassic reptiles and dinosaurs of the Transantarctic Mountains (Collinson and Hammer, 2007; Smith et al., 2007).
For the last 100 million years, from the Late Cretaceous onward, the Antarctic continent has been situated over the South Pole in approximately its present location. In sharp contrast to current frigid polar conditions, abundant sub-tropical fossil plants are commonly found in Antarctic rocks. The subtropical nature of these fossil plants indicates warm, humid climates at high latitudes during the mid-Cretaceous (Francis et al., 2008, this volume). A variety of dinosaurs lived in these polar forests, as shown by the wealth of bones collected from the Antarctic Peninsula region. The Late Cretaceous dinosaur fauna is a relict of a cosmopolitan dinosaur assemblage that survived until the end of the Cretaceous in Antarctica after becoming extinct elsewhere (Case, 2007). Discoveries of juvenile marine reptile fossils indicate that Antarctica may have been a nursery for young marine reptiles (Martin et al., 2007).
The plant record reveals an interesting conundrum about the terrestrial response to the major climate transition from greenhouse to icehouse during the latest Eocene-earliest Oligocene. Analyses of fossil leaf collections from the Antarctic Peninsula show a temperature decline from warm temperate to cold climates through the Eocene. These cold Eocene climates may have had winter frosts coinciding with a decline in plant diversity (Francis et al., 2008, this volume). A similar cooling trend dominates the marine isotope record. In contrast, the offshore pollen record, recovered from Integrated Ocean Drilling Program (IODP) cores, indicates only short-term responses to individual cooling events and fairly