Pedogenic iron-manganese nodules in Vertisols: A new proxy for paleoprecipitation?

The total Fe content of pedogenic iron-manganese (Fe-Mn) nodules taken from a Vertisol climosequence on the Texas Gulf Coastal Plain correlates with mean annual precipitation (MAP, r(2) = 0.92). No significant trend of total Fe (Fe-TOT) with depth was noted in profiles. Using the regression developed from modern Vertisol data, Fe-TOT contents of Paleozoic paleo-Vertisol Fe-Mn nodules yielded MAP regimes comparable to previously inferred paleoenvironmental interpretations. Paleoprecipitation estimates derived from Fe-Mn nodules for an uneroded, Late Mississippian paleo-Vertisol are very close to estimates determined from a depth to pedogenic carbonate horizon (DCH) proxy determined from the modern Vertisol climosequence. The lack of soil depth dependence of the Fe-Mn nodule proxy provides a consistent paleoprecipitation estimate even in eroded paleo-Vertisols and, in combination with the DCH, may be useful in determining original paleosol thickness.