Magnetic susceptibility variations observed in Quaternary loess sequences of China have been linked to pedogenesis and used to characterize terrestrial climatic variations through glacial-interglacial transitions. To date, however, magnetic studies of loess sequences have been applied exclusively to Quaternary deposits. Here we demonstrate preservation of magnetic susceptibility variations in an upper Paleozoic loessite sequence of western North America. Magnetic susceptibility through a continuously exposed test section of the loessite varies by more than an order of magnitude: low values occur in unaltered loessite horizons, and high values are found in sedimentologically confirmed or suspected paleosol horizons. Low-temperature remanence and hysteresis data indicate that the susceptibility variations between paleosol and loessite horizons relate to differences in concentration and grain size of the magnetic carrier. These results are consistent with in situ formation of ultra-fine-grained (superparamagnetic) material during pedogenesis. We suggest that these susceptibility variations relate to periodic pedogenesis linked to late Paleozoic climatic fluctuations in low latitudes of western Pangea.

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