Peatland ferruginization during late Quaternary in the Uberaba Plateau (South-Eastern Brazil) Jean Dominique Meunier a, * , Angelica F.D.C. Varajão b , Cesar A.C. Varajão b , Fabrice Colin a , Olivier Grauby c a Aix-Marseille Université, CNRS, IRD, CEREGE UM34, 13545 Aix en Provence, France b DEGEO/EM/UFOP, Campos Morro do Cruzeiro, 35400-000 Ouro Preto, MG, Brazil c Aix-Marseille Université, CNRS, CINaM, Campus de Luminy Case 913, 13288 Marseille, France article info Article history: Received 18 January 2012 Accepted 20 December 2012 Keywords: Peatland Iron duricrust Brazil Latosol Oxidation Carbon dynamics Climate change abstract Due to the poor preservation of old peat formations and the limited research developed on them, the contribution of peat oxidation to the global C cycle at geological scales is poorly understood. Iron dur- icrusts containing abundant well-preserved plant structures have been reported above Humic Gleysols in the Uberaba Plateau (Brazil). We show that the iron accumulation results from an in-situ impregnation of peat, fast enough to preserve the plant structures. The formation of iron oxides results from two pro- cesses: precipitation in the pores and C/Fe replacement. The iron duricrusts were probably triggered by oxidation of the peatland following dry climatic events during the last 50 kyr. The large amount of iron dissolved in peatland waters was immobilized contemporaneously with the destruction of organic matter. The oxidation of organic matter from the lower peat, dated at ca 24e27 kyr BP, may have released between 0.08 and 2.26 kg CO 2 m 2 yr 1 in the atmosphere. These rates are in a good agreement with present-day measurements of CO 2 release from drained peatlands. Although peatland formation has been identified as a significant contributor to the global CO 2 uptake, our findings suggest that natural peatland oxidation should also be considered as a source of atmospheric CO 2 during past climate change. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The oxidation of organic matter from peatland has become a major global concern because it can release significant CO 2 into the atmosphere (Limpens et al., 2008; Joosten, 2009; Sorensen, 1993; Evans and Lindsay, 2010). Although the impact of peatland accumulation on climate radiative forcing is significant at the long- term scale (i.e. for Holocene: Frolking and Roulet, 2007), the con- sequences of environmental change on peatland oxidation is so far not documented by any paleosol or sedimentological data. The preservation of plants remnants requires a rapid replacement by an inorganic solid phase before destruction of the organic material (Pailler et al., 2000; Akahane et al., 2004). Such a fossilization is a priori not favorable to the preservation of peat features in an oxidizing environment. However, plant fossils are sometimes encountered in lateritic duricrusts (Grandin and Perseil, 1977; Varajão et al., 2002, 2007) suggesting a replacement of carbon features by minerals stable in oxidizing environment such as iron oxides. Goethite and hematite are two common minerals in iron dur- icrusts that are known to develop under tropical climate with strong seasonality (Tardy, 1993). Two mechanisms are proposed to explain the enrichment of these minerals in the iron duricrusts (Nahon, 1991; Thomas, 1994): 1) in-situ enrichment by weathering of iron-rich parent rocks, 2) lateral migration of Fe 2þ in reduced or acid solutions and accumulation of Fe 3þ oxides at the interface with an oxidizing, neutral to alkaline environment. Vegetation cover and biological activity in soil are assumed to play an important role in leaching iron from rocks through the local reduction of iron around roots where pH is lowered. Therefore, if iron is sufficiently mobi- lized in a peatland, any environmental changes leading to oxidation and destruction of peatland would be favorable to precipitation of iron oxides. The objective of this paper is to document this scenario as well as its consequences for CO 2 release into the atmosphere. At Uberaba Plateau (South-Eastern, Brazil), Varajão et al. (2002, 2007) reported on an iron duricrust containing plant fossils above a peat layer which may indicate peat oxidation and fossilization by * Corresponding author. E-mail address: meunier@cerege.fr (J.D. Meunier). Contents lists available at SciVerse ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames 0895-9811/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsames.2012.12.004 Journal of South American Earth Sciences 43 (2013) 25e32