2006 Philadelphia Annual Meeting (22–25 October 2006)

Paper No. 9
Presentation Time: 10:00 AM


BLAKEY, Ronald C., Geology, Northern Arizona University, Box 4099, Flagstaff, AZ 86011, ronald.blakey@nau.edu

The 450 million-year-long fragmentation of Gondwana ranks as one of the dominant Phanerozoic tectonic events. Following assembly during the Late Proterozoic, the megacontinent began to shed a series of sliver-like peri-Gondwanan terranes. The rifting process began in the Cambro-Ordovician and continued throughout most of the Mesozoic. Gondwana lost approximately 20% of its mass through this process as the Avalon, Hun, Sino, Cimmeria, and other terranes drifted northward. Major phases of the Caledonian, Variscan, Ouachita-Marathon, and Cimmerian orogenies were generated as peri-Gondwanan slivers slammed into the northern continents. Today these terranes stretch across southern and eastern North America, southern Europe, and southern and eastern Asia. During the Jurassic, the core of Gondwana still held together as western Gondwana rifted from Laurasia and the North Atlantic Ocean and Gulf of Mexico opened. By the mid Cretaceous, the fate of Gondwana was sealed as east and west Gondwana began to rift apart; as the South Atlantic opened, Africa rifted from South America and India sped northward forming the Indian Ocean in its wake. In the early Cenozoic, Antarctica split from Australia and Gondwana was geologic history.

Because Gondwana fringed the South Pole during most of the above history, standard rectangular and oval global projections show much of it distorted; tectonic and other paleogeographic features are difficult to visualize and the overall geologic history is less well known than that of Laurasia. By manipulating standard rectangular global projections into spherical (orthographic) projections using Flexify®, a Photoshop® plug-in, spherical projections can be oriented in any manner and the paleogeographic history of polar regions can be clearly shown with minimal distortion. Thus displayed, the paleogeographic patterns of “down under” dynamically unfold.