Pedogenic carbonate proxies for amount and seasonality of precipitation in paleosols

Abstract

The dept to carbonate nodular (Bk) horizon in soils (D in cm) is correlated with mean annual precipitation (P in mm), so that Bk horizons are deep in subhumid regions, but shallow in semiarid regions. Previous quantifications of this relationship are unchanged by this new compilation of 807 soils: P = 137.24 + 6.45D + 0.013D2, where R2 = 0.52, and standard error (S.E.) = ±147 mm. In most North American postg1acial soils, the Bk horizon is thin and well defined, whereas in monsoonal tropical soils of Pakistan and Kenya, the Bk horizon is thick and diffuse. Data from 675 modern soils define the relationship between the thickness of soil with nodules (T in cm) and mean annual range of precipitation (M in mm difference between monthly means of wettest and driest months): M = 0.79T + 13.71, where R 2 = 0.58, and S.E. = ±22 mm). The relationship between carbonate nodule size (S in cm) and soil age (A in ka) is quantified by 9 radiocarbon-dated soils from Las Cruces, New Mexico: A = 3.92S0.34, where R2 = 0.57, and S.E. = 1.8 k.y. These transfer functions are applied to reconstructing paleoclimatic change from Paleocene-Eocene paleosols of the North Horn Formation and Flagstaff Limestone of Axhandle Canyon, Utah. The terminal Paleocene spike of warmth recorded by fossil plants in nearby Wyoming was coincident with a brief peak in both mean annual precipitation and mean annual range of precipitation in Utah. © 2005 Geological Society of America.