64-3 Developing a New Paleoprecipitation Proxy using Micro-XRF of Soil Ferromanganese Nodules

Session: Emerging Voices in Soil and Paleosol Science (Posters)

Presenting Author:

Authors:

Abstract:

Paleosol bulk geochemistry combined with various modeling techniques (CIA-K, CALMAG, PPM, & RFMAP) is a common approach used to predict paleoclimates and reconstruct past soil-forming conditions. These models use bulk geochemistry from subsoil B horizons to predict past climate. The models assume that geochemistry tracks pedogenesis as a function of climate. However, the bulk geochemistry of those same subsoil horizons may reflect environmental factors (e.g., parent material) other than climate. Analysis of pedogenic features, e.g., ferromanganese nodules (FMN) and pedogenic carbonates, shows greater promise as these features are more directly linked to the long-term soil hydrologic cycle and climate. This study revisits a Texas Vertisol climosequence and uses non-destructive analysis of FMN via micro-XRF spectrometry to more thoroughly investigate the influence of precipitation on these pedogenic features. We measured the concentration of Fe and Mn in FMN from center to edge using an Atlas X micro-XRF spectrometer at a 5 µm resolution. Three sites with differing mean annual precipitation and soil moisture regimes (SMR) were studied: Victoria Series (894 mm, Ustic SMR), Lake Charles Series (1,124 mm, Udic SMR), and League Series (1,411 mm, Oxyaquic Udic SMR). We focused on Fe and Mn due to their high concentration and position on the redox ladder: Mn (suboxic), Fe (anoxic). Preliminary findings have replicated previous work correlating Fe quantity with rainfall. We also found that the maximum Fe/Mn ratio, located along the outermost edge of nodules across all sites, positively correlates with mean annual rainfall. We interpret this maximum Fe/Mn along nodule edge to reflect an open system where long-term integration of saturation history becomes more anoxic (i.e., higher maximum Fe/Mn) with increasing mean annual rainfall. These results will be used to develop a new paleoprecipitation proxy applicable to paleo-Vertisols containing FMN.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8134

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.