Is there a possibility to correct fossil n-alkane data for postsedimentary alteration effects? Björn Buggle a, * , Guido L.B. Wiesenberg b , Bruno Glaser a a Soil Physics Department, University of Bayreuth, D-95440 Bayreuth, Germany b Agroecosystem Research Department, University of Bayreuth, D-95440 Bayreuth, Germany article info Article history: Received 24 August 2009 Accepted 6 April 2010 Available online 10 April 2010 Editorial handling by R. Fuge abstract The long chain n-alkane composition of plant material can significantly differ between plant groups e.g. trees and grasses. Due to their relative recalcitrance, they have been employed in paleoecological research as molecular proxies for different types of vegetation. Most of those paleoenvironmental studies rely on the assumption that characteristic molecular fingerprints of plant material are preserved in the fossil organic material without significant alteration. However, there exists evidence that n-alkane distri- butions may change in the course of plant litter degradation. Here, the authors propose and discuss a con- ceptual approach to the correction of n-alkane patterns in paleosols and terrestrial sediments for postsedimentary alteration effects. This might have potential to improve paleoenvironmental reconstruc- tions derived from these molecular fossils. In soil depth profiles typically a correlation between the OEP (odd over even predominance) and paleoecological valuable long-chain n-alkane ratios (LARs) can be found. Similar relationships have been also obtained from n-alkane records in paleosols. With the OEP serving as a proxy of microbial reworking, the correction procedure applies OEP vs. LAR regression func- tions to correct fossil LARs for degradation effects. The regression functions have been derived from mod- ern soils. The application of the procedure and its significance for paleoecological interpretations is demonstrated on a case study of a loess-paleosol sequence (400–700 ka) in Romania. It is shown that changes in the C27/C31 n-alkane ratio at this site are closely related to degradation effects rather than to changes in the paleovegetation (e.g. tree vs. grass abundance). However, it was found that the C29/ C31 ratio is a more suitable paleoenvironmental proxy at the Mircea Voda site. The results indicate that there is a future potential to correct fossil n-alkane ratios via the OEP/LAR relationship, however at the moment a general straight forward application of this approach might be critical due to lack of extended and diverse n-alkane records from modern soils. The need of more systematic n-alkane studies on soil profiles is highlighted to improve knowledge concerning dynamics and actual mechanisms of postsedi- mentary LAR and OEP changes. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Long-chain n-alkanes (>C25) with a pronounced dominance of odd over even homologues are essential components of plant cuticular lipids (e.g. Eglinton and Hamilton, 1967). As such they are transferred to the soil surface in course of litterfall, eventually blown or washed into rivers and finally buried in lacustrine or mar- ine sediments. A significant part of leaf-derived lipids will enter the soil organic matter (SOM), which is subsequently either eroded, degraded or buried in situ. If preserved in sedimentary archives, these compounds represent valuable molecular fossils (e.g. Eglinton and Eglinton, 2008). It has been shown that cuticular lip- ids have a potential for the chemotaxonomical differentiation of plants (e.g. Eglinton et al., 1962; Stevens et al., 1994; Maffei 1996a). However due to inter- and intraspecies variability, their chemotaxonomical value is restricted and mostly allows only a rough differentiation of different plant groups (Borges del Castillo et al., 1967; Schwark et al., 2002). Nevertheless, their relative recal- citrance makes long chain n-alkanes an especially attractive tool in paleoenvironmental studies. Thus, they are used e.g. to distinguish between tree- or shrub-derived plant material with a predomi- nance of mostly n-C27 or n-C29 and grasses with mostly n-C31 or n-C33 dominance (Cranwell, 1973; Meyers and Ishiwatari, 1993; Maffei, 1996a,b; Zhang et al., 2008; Zech et al., 2009b). Hence these compounds are regarded as biomarkers and their ra- tios (e.g. C27/C31, C29/C31, (C27 + C29)/(C31 + C33)) are applied as proxies for the source determination of fossil organic material e.g. trees (shrubs) vs. grasses (e.g. Schwark et al., 2002; Zhang et al., 2006; Bai et al., 2009; Zech et al., 2009). The motivation of using n-alkanes in studies of fossil soils is – beside their relative recalcitrance – their complementarity to other methods such as 0883-2927/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.apgeochem.2010.04.003 * Corresponding author. Fax: +49 (0)921 552247. E-mail address: Bjoern.Buggle@uni-bayreuth.de (B. Buggle). Applied Geochemistry 25 (2010) 947–957 Contents lists available at ScienceDirect Applied Geochemistry journal homepage: www.elsevier.com/locate/apgeochem