Friday, November 23, 2007

As The World Turned

Inconsistencies Between Pangean Reconstructions and Basic Climate Controls. 2007. C. M. Rowe, et al. Science 318: 1284 – 1286.

The supercontinent Pangea dominated our planet from the Permian into the Jurassic. Paleomagnetic reconstructions have been used to estimate the atitudinal position of Pangea during this 100-million-year period.

Atmospheric circulation, recorded by eolian sandstones in the southwestern United States, shows a broad sweep of northeasterly winds over their northernmost extent, curving to become northwesterly in the south: This evidence is consistent with paleomagnetic reconstructions of the region straddling the equator in the Early Permian but is at odds with its northward movement to about 20°N by the Early Jurassic.

At least one of the following scenarios must be true:

- The latitude based on paleomagnetism is incorrect; the interpretation of how winds shaped the dunes is mistaken;

- the basic climate controls in the Jurassic were different from those of today;

- or the paleogeographic reconstructions available are insufficient to adequately reproduce the wind fields responsible for dune formation.