Geology

Pangea Weather Report

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Science  16 Aug 2002:
Vol. 297, Issue 5584, pp. 1095
DOI: 10.1126/science.297.5584.1095b

The final assembly of the supercontinent Pangea, toward the end of the Paleozoic Era, built up an enormous, high-standing land mass that straddled Earth's equator. Those were excellent conditions for the development of a monsoon in the supercontinent's equatorial regions, and paleoclimate models have suggested that a transition from zonal to monsoonal circulation patterns had probably taken place by the early Permian Period, approximately 280 million years ago.

Now Soreghan et al. present some persuasive geological evidence for such a transition. They employed an ingenious tracer: the isotopic ages of detrital zircons in Upper Paleozoic loessites (rocks formed from deposits of windblown silt) in the southwestern United States, which marks the late Paleozoic location of western equatorial Pangea. Tying the isotopic ages to regional source rocks exposed during the late Paleozoic, they inferred predominant northeasterly winds during the middle Pennsylvanian Period (290 to 300 million years ago), but a combination of westerly and easterly wind patterns during the early Permian, a pattern consistent with a shift from zonal circulation to a seasonal monsoon. — SW

Geology30, 695 (2002).

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