Palynofacies and organic geochemistry studies of organic matter from a wetland system of southern Brazil influenced by different hydrological regimes in the Quaternary Gabrielli Teresa Gadens-Marcon a, b, * , Margot Guerra-Sommer a , Jo ~ ao Graciano Mendonça-Filho c a Instituto de Geoci^ encias, Universidade Federal do Rio Grande do Sul, 91501-970 Porto Alegre, RS, Brazil b Universidade Estadual do Rio Grande do Sul, 90010-191 Porto Alegre, RS, Brazil c Instituto de Geoci^ encias, Universidade Federal do Rio de Janeiro, 21949-900 Rio de Janeiro, RJ, Brazil article info Article history: Received 3 March 2013 Accepted 6 August 2014 Available online 28 August 2014 Keywords: Continental environment Organic matter Total organic carbon Total sulfur Peaty sediments Water table abstract The main goal of this study was to quantitatively and qualitatively characterize the sedimentary organic matter (OM) and demonstrate the usefulness of geochemistry and palynofacies analysis for obtaining paleoenvironmental data for the Holocene in southernmost Brazil. The results indicate that during the time interval from 10,586 cal yr BP to the present, the study area housed a wetland characterized by different hydrologic regimes. The basal peaty deposits correspond to a phase influenced mainly by the groundwater table, whereas the upper deposits composed of silty organic mud indicate fluvial influence related to river overflow events. In a similar manner, the TOC (total organic carbon) and TS (total sulfur) contents are higher in the basal portion of the profile, decreasing toward the top. These findings could be related to granulometry alterations that are linked to hydrologic regimes or anthropogenic interference in the landscape dynamics. Anomalous TS content observed in one of the samples might be due to an external source and perhaps related to the presence of thermal springs in the region. These types of areas have potential as a modern reference that can be applied in the reconstruction of past analogous en- vironments such as coal deposits associated with fluvial paleoenvironments. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Wetlands are important ecosystems that are favorable for organic matter preservation and peat accumulation (Clymo, 1983). The characterization of currently existing peaty areas is established according to the nature of the water resources, the origin and na- ture of sedimentary particles supply and the local ecological supply (Mesnage et al., 2002). Studies of Holocene peats have been improved because of their sensitivity to environmental changes caused by climate and human impacts (Sebag et al., 2006a). As wetlands, and particularly peaty sediments, are important areas for organic matter storage, studies based on organic geochemistry and palynofacies analyses of these types of Holocene deposits allow the identification of relationships between distinct organic patterns with their corresponding depositional environment. According to Tyson (1995), the advantage of applying the palynofacies technique lies in the fact that it provides direct information about the origin and characteristics of the particulate organic matter, allowing a more detailed analysis of subtle variations in the sedimentary environment. Much of the interpretive models available in the scientific literature that concern organic geochemical and palynofacies analysis were designed for use in marine and epicontinental sec- tions with the main objective being the exploration of hydrocarbon source rocks. Although relatively recently developed, palynofacies analyses have been applied to different depositional systems, resulting in a powerful research tool used to characterize the OM of present-day samples in continental deposits (Lorente, 1986, 1990a,b; Caratini, 1994; Gastaldo, 1994; Rull, 1995; Gastaldo et al., 1996; Di-Giovanni et al., 1999; No€ el et al., 2001; Gastaldo and Huc, 1992; Cohen et al., 1999a,b; Sebag et al., 2006a,b), coastal environments (Marchand et al., 2003; Sparica et al., 2005; Prasad et al., 2007) and marine deposits (Lallier-Verg es et al., 1993; Van Waveren and Visscher, 1994; Lückge et al., 1996; Vald es et al., 2004; Lallier-Verg es and Alb eric, 1990). * Corresponding author. Instituto de Geoci^ encias, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves, n  . 9500, Pr edio 43127, Sala 201, Campus do Vale, 91501-970 Porto Alegre, RS, Brazil. E-mail addresses: gabigadens@yahoo.com.br (G.T. Gadens-Marcon), margot. sommer@ufrgs.br (M. Guerra-Sommer). Contents lists available at ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames http://dx.doi.org/10.1016/j.jsames.2014.08.002 0895-9811/© 2014 Elsevier Ltd. All rights reserved. Journal of South American Earth Sciences 56 (2014) 41e53