64-2 Linking Climate and Pedogenic Carbonates using Benchtop Micro-XRF Analysis: A Case Study from the Serengeti National Park

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

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Pedogenic carbonates (PC) are crucial for understanding both current and past environments. However, knowledge about the geochemistry of PC formation in savanna ecosystems remains limited. Here, we employ micro-X-ray Fluorescence (micro-XRF) to investigate the chemistry of PC, aiming to understand alkaline soil development at the micron scale. We examined PC collected at a depth of 40-50 cm from a transect across the Serengeti Ecosystem where mean annual precipitation (MAP) ranges from 832 mm/yr at Nyaruswiga to 558 mm/yr at Shifting Sands. X-ray spectra were extracted from zones of maximum calcium concentration in PC samples, assuming these zones represent pedogenic CaCO₃ with minimal parent material or soil matrix interference. The PC from the wetter Nyaruswiga contains higher mean concentrations of Mg and K but are within error of the concentrations measured at the drier Shifting Sands. We hypothesize that higher concentrations of Mg and K at Nyaruswiga may reflect a change in parent material, where this source material may have an overall higher extractable Mg and K content that is now reflected in the CaCO₃. The PC from Nyaruswiga has lower mean Mn concentration, but within error of Shifting Sands. The Fe concentration is significantly higher at Nyaruswiga than at Shifting Sands. We hypothesize that the ratio of these two redox-sensitive elements, Fe/Mn, reflects saturation conditions leading up to, and during, PC formation. Higher, more variable Fe/Mn at Nyaruswiga suggests this soil experienced wetter, more prolonged anoxic conditions that mobilized more Fe and enriching it in the PC. Lower Fe/Mn recorded at Shifting Sands suggests sub-oxic conditions may have prevailed during PC formation, where Mn was mobilized and enriched in PC. These redox patterns are inferred to reflect the hydroclimatic conditions at each site, where the wetter Nyaruswiga had more prolonged soil saturation and anoxic conditions than at the drier Shifting Sands. Future work will test these trends as we analyze additional sites across this transect of the Serengeti Ecosystem. Our preliminary work suggests that the micro-XRF analysis of Fe/Mn from soil carbonates holds promise in deciphering the soil moisture conditions and climate.

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

doi: 10.1130/abs/2025AM-8128

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