An analysis of 1168 modern soil profiles from the U.S. Natural Resources Conservation Service yields no correlation between mean annual precipitation and depth to the top of the carbonate horizon (r2 = 0.03; p < 0.001). Parent material and soil texture both play negligible roles in this regression. When combined with similar published studies (n = 1481), r2 improves slightly (r2 = 0.31; p < 0.001). Caution is therefore advised in using this or any previously published regression for inferring paleoprecipitation from paleosols. However, in the combined data set, carbonate horizon–bearing soils correlate with a mean annual precipitation of < 760 mm (p < 0.05). Thus the presence vs. absence of pedogenic calcium carbonate is a good indicator of paleoprecipitation above or below this value.

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