Reassessment of the Microbial Role in Mn-Fe Nodule Genesis in Andean Paleosols

Abstract

The presence of Mn-Fe nodules in the epipedons (surface horizons) of paleosols of presumed Upper Neogene age in the northwestern Venezuelan Andes have been interpreted as products of inorganic oxidation and reduction processes operating over the full range of glacial and interglacial cycles that affected paleosol morphogenesis. New microscopic/chemical data from combined SEM-EDS-FIB analyses of representative Mn-Fe nodules indicate microbes play an important role in Mn/Fe precipitation leading to their genesis in alpine Mollisols (Argiustolls). Although the prevailing new data are based mainly on fossil forms of filamentous bacteria and fungi and other biogenic pseudomorphs that may represent the former resident bacteria, the presence of extant microbes must await field experiments/collection, followed by a molecular microbiology approach to determine the biological drivers of metal precipitation. As in other terrestrial niche environments, microbes are seen here to play a role, perhaps a key one, in the morphogenesis of paleosols of importance in upper Neogene paleoenvironmental reconstruction.

Keywords:

• Andean paleosols
• microbial assisted soil nodule growth
• Mn nodules
• redox role in nodule genesis reassessed

Additional information

Funding

This research was funded by Quaternary Surveys, Toronto, and the Garage Institute. The CAMCOR High-Resolution and Nanofabrication Facility (TEM, FIB, and SEM) are supported by grants from the W. M Keck Foundation, the M. J. Murdock Charitable Trust, and ONAMI, the Air Force Research Laboratory (agreement number FA8650-05-1-5041), NSF (award numbers 0923577, 0421086 ) and the University of Oregon.