Dust and Loess Deposits in Late Paleozoic Pangaea
Which way did the winds blow? How dusty was the atmosphere? How did dust influence the biosphere, and geochemical cycling? Atmospheric circulation in the supercontinent of Pangaea is thought to have been dramatically different from that of today, likely characterized by “megamonsoonal” conditions and, at times, a remarkably dusty atmosphere. We are studying sources of ancient eolian siltstone (paleo-loess) in North America and elsewhere to reconstruct atmospheric dustiness, paleoatmospheric circulation, and dust-induced biotic effects 300 million years ago. Approaches include field work to log and sample sections, and a variety of analytical approaches such as petrography, particle-size analysis, whole-rock and isotope geochemistry (aided by colleagues) and detrital-zircon geochronology for provenance analysis. We apply these data as proxies for wind directions and strengths, enabling us to gauge evolution of equatorial winds during the onset of the Pangaean megamonsoon, and glacial-interglacial shifts in atmospheric dustiness.