Evaluating Trace Elements as Paleoclimate Indicators: Multivariate Statistical Analysis of Late Mississippian Pennington Formation Paleosols, Kentucky, U.S.A.

Abstract

The temporal and spatial distributions of trace elements in paleosols in relation to soil‐forming processes and climate have received little attention, primarily due to their generally low concentrations (<100 ppm) and a fundamental lack of knowledge of their behavior in soil systems. Trace element concentrations of Pennington Formation paleosols, spanning an 8‐Ma interval in the Late Mississippian (Chesterian), were analyzed using linear and multivariate statistics of whole‐rock elemental data. Linear statistics of the elemental data set show that Ti, Zr, Nb, Cs, La, Hf, Ta, W, Ce, and Th have the highest correlation through time, with r values ≥0.75. Nb served as the proxy trace element for comparison. Temporal trends in Nb closely match trends in lessivage (clay formation and accumulation by feldspar weathering), mean annual precipitation (MAP), and chemical weathering. MAP effectively controls soil hydrology and the accumulation of organic matter and clay. MAP, in conjunction with chemical weathering, controls trace element accumulation. Fe and Mn concentrations provide conflicting evidence and raise the question of whether redox conditions act as a fundamental control. Trace element concentrations through time identify high‐frequency Late Mississippian climate changes, characterized by extreme wet and dry periods. In addition, cluster analysis and discriminant analysis, using canonical variates, of trace elemental data were able to distinguish between soil orders and, to a lesser degree, soil drainage conditions. The use of multivariate statistical analysis in a temporal study of paleosol trace element chemistry therefore provides a new tool to evaluate pedogenic processes and a means by which to draw inferences regarding intensity of chemical weathering and its relationship to climate change.