Article

Inventory of sedimentary organic matter in modern wetland (Marais Vernier, Normandy, France) as source-indicative tools to study Holocene alluvial deposits (Lower Seine Valley, France)

Article

Inventory of sedimentary organic matter in modern wetland (Marais Vernier, Normandy, France) as source-indicative tools to study Holocene alluvial deposits (Lower Seine Valley, France)

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Abstract

Palynofacies' analysis was developed for petroleum exploration, but it is now commonly used to differentiate the major constituents of the sedimentary organic matter (SOM) in Postglacial deposits. Our work aimed at studying the SOM distribution in a present wetland of the Seine estuary (Vernier Marsh) in order to provide comparative elements to interpret the composition of SOM in the Lower Seine Valley alluvial infilling. In the Vernier Marsh, the distribution of major constituents is heterogeneous. Thus, for each depositional environment studied (soils, drainage ditches, channels, ponds), the composition of SOM has been characterized by using two ternary diagrams ("Amorphous OM/Preserved Phytoclasts/Transformed Phytoclasts" and "Opaque/Amorphous/Gelified Particles"; OP/AP/GP). This approach allowed us to define four optical indices that can be used to estimate the relative abundances of principal organic fractions in mixed deposits based on the origin of SOM (aquatic/terrestrial), its source areas (vegetation, soils, river), and controls of early diagenetic changes (aerobic/anaerobic conditions, advanced oxidation). "Amorphous OM contents" increase from terrestrial environments to fluvial deposits and evaluate the abundance of planktonic contribution. "Preserved / transformed phytoclasts ratio" decreases from sites of production to those of deposition indicating the degree of degradation of terrestrial materials. "OP contents" allow one to define fluvial (high values) and palustrine (low values) environments. "GP / AP ratio" allows one to discern soil (low values) and plant (high values) supplied areas. Finally, these optical compositional indices are measured in Holocene deposits and used to complete palaeoenvironmental reconstructions.

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... In fact, all these techniques are used to quantify the micrometric heterogeneity of the particulate OM (Tyson, 1995). In this way, recent works showed that the palynofacies analysis could be used to characterize the OM of present-day samples: soil layers (Di-Giovanni et al., 1999a ), lacustrine sediments (Noël et al., 2001), palustrine and alluvial deposits (Gastaldo and Huc, 1992; Cohen et al., 1999; Sebag et al., 2006b), coastal environments (Marchand et al., 2003; Sparica et al., 2005), upwelling deposits (LallierVergès et al., 1993a; Lückge et al., 1996; Valdés et al., 2004; Pichevin et al., 2004) and deep-sea pelagic sediments (Vergès and Albéric, 1990; van Waveren and Visscher, 1994). Thus, the palynofacies method is well known and classically applied by petroleum geologists, sedimentologists and by Quaternary scientists who study palaeoenvironments and climate changes. ...
... biodegradation, combustion, weathering). For example, this approach was performed for the correlation between changes in OM composition and environmental , climate and/or land use changes in various contexts as Alpine and Andean lakes (Buillit et al., 1997; Sifeddine et al., 1998; Noël et al., 2001), tropical and temperate wetlands (Sifeddine et al., 1995; Bourdon et al., 2000; Sebag et al., 2006b ), and streams from submediterranean mountains (Martaud, 2003). 3.1.1. ...
... In this study, the author uses the relative proportions (1) of phytoclasts and sporomorphs to determine the influence of terrestrial inputs, (2) of AOM to determine oxic/anoxic regime and (3) of zoomorphs to reconstruct the distance from the shoreline. Furthermore , it is successfully applied to track the changes in the OM composition during the humification in soil profiles (Di-Giovanni et al., 1998), the diagenesis of peaty deposits (Bourdon et al., 2000), the transport of reworked terrestrial particles (Di-Giovanni et al., 2000b; Sebag et al., 2006b) or the weathering of geological substratum (Di-Giovanni et al., 1997; Martaud, 2003). This kind of studies based on optical markers and petrographical signatures improves the knowledge of present-day and modern environments. ...
Article
Palynofacies analysis is based on transmitted light microscope study of organic constituents isolated and concentrated by acid and basic digestions. Published results of studies of present-day terrestrial environments show that two complementary approaches successfully characterize particulate organic matter (OM) from palynofacies analyses. The first method is based on the identification and the quantification of some typical particles (optical markers) according to their origin (i.e. aquatic or terrestrial), their nature (i.e. biogenic, anthropogenic, fossil), and/or their formation (i.e. biodegradation, combustion, oxidation). The second approach is based on the use of binary or ternary diagrams in order to define petrographical signatures from the relative proportions of significant organic constituents. This approach can be used for tracking i) changes in OM composition during humification in soil profiles, ii) transport of reworked terrestrial particles, iii) diagenesis of peaty deposits, or iv) weathering of geological substratum. The more advanced approach is based on the use of some predefined optical markers and their optical signatures to establish the relation between the OM compositions (palynofacies) and their depositional environments. In addition, this kind of study aims to define a modern frame of reference that can be applied in paleoenvironmental reconstructions . This paper combines a bibliographic review with previously unpublished data from palynofacies analyses. The aim is to present some applied examples illustrating (1) the main approaches developed for characterization of the particulate OM in surficial deposits, and (2) the study of OM transfers in terrestrial geosystems.
... Photomicrographs were taken using an AmScopeTM camera adapter connected to the AmScope v.3.7 camera software and Leica MC190 HD camera connected to the Leica LAS EZ software. The palynofacies analyses were performed according to the classifications proposed by Tyson (1995) and Sebag et al. (2006). Three categories of organic matter (OM) were used: (1) phytoclasts: opaque phytoclasts (OP) and ligno-cellulosic debris (LcD), which can be preserved as cuticles and membranes (CM), transparent (TLC), altered (ALC), amorphous (AP) or gelified particles (GP), (2) Amorphous organic matter (AOM) and (3) palynomorphs. ...
... The silty matrix within the Bd facies is the result of secondary infiltration (e.g., Martini, 2011) due to the existence of occasional and relatively insignificant water flow within the open cave channel. This is evidenced by the preserved/transformed phytoclast ratio according to Sebag et al. (2006). Even though this index was introduced by Sebag et al. (2006) for Holocene alluvial sediments, our data show a distribution of the index (Figure 10) which allows us to distinguish the paleoenvironment, confirming a transition from a fluvial paleoenvironment in the lower (older) part of the section (DC-SP 1-Bd facies) to a non-aquatic terrestrial paleoenvironment toward the youngest part of the section (DC-SP 8-Late Bronze Age). ...
... This is evidenced by the preserved/transformed phytoclast ratio according to Sebag et al. (2006). Even though this index was introduced by Sebag et al. (2006) for Holocene alluvial sediments, our data show a distribution of the index (Figure 10) which allows us to distinguish the paleoenvironment, confirming a transition from a fluvial paleoenvironment in the lower (older) part of the section (DC-SP 1-Bd facies) to a non-aquatic terrestrial paleoenvironment toward the youngest part of the section (DC-SP 8-Late Bronze Age). Such interpretation shows a good correlation with the sedimentological data. ...
Article
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During archeological excavations in the Lower Cerovačka Cave (Mt. Velebit, Croatia), the test trench penetrated to a depth of 1.8 m. An undisturbed sequence of sediments was exposed. Considering that caves represent highly efficient sediment traps it was possible to recognize changes in the depositional mechanisms during the Pleistocene-Holocene period. Using the multiproxy approach, the mineralogical, petrographic, and biostratigraphic characterization of the cave sediments was performed. Facies analysis revealed several stages in the development of the clastic filling of cave channels. Allochthonous origin of the sediment was assumed. Sedimentation took place under various conditions from pronounced cold and dry climate during Pleistocene stages in the base of the profile, to humid periods with anthropogenic influence during the Holocene at the very top of the profile. Although traditionally these sediments were believed to be of Pleistocene age, here for the first time a stratigraphic calibration of the profile has been performed based on luminescence dating of detrital cave sediments and radiometric dating of speleothems.
... According to Batten (1996), most cuticles identified in palynological slides are derived from leaves, and are generally associated with fluvial-deltaic environments of low energy, from where they can be transported over long distances prior to destruction or deposition. However, the cuticles identified in this core are well preserved, suggesting that their deposition most likely occurred near the source Un-biostructured phytoclasts, identified in some studies (Sebag et al., 2006a(Sebag et al., , 2006bBoussafir et al., 2012;Zocatelli et al., 2012) as gellified particles, have their origin related to plant tissue degradation in aquatic environments, such as lakes, or under anaerobic conditions, such as in hydromorphic (excess water) soils (Sebag et al., 2006a). Biostructured phytoclasts are described as originating from local vegetation (Tyson, 1995), but they can also be deposited in river channels during flooding (Batten, 1996). ...
... According to Batten (1996), most cuticles identified in palynological slides are derived from leaves, and are generally associated with fluvial-deltaic environments of low energy, from where they can be transported over long distances prior to destruction or deposition. However, the cuticles identified in this core are well preserved, suggesting that their deposition most likely occurred near the source Un-biostructured phytoclasts, identified in some studies (Sebag et al., 2006a(Sebag et al., , 2006bBoussafir et al., 2012;Zocatelli et al., 2012) as gellified particles, have their origin related to plant tissue degradation in aquatic environments, such as lakes, or under anaerobic conditions, such as in hydromorphic (excess water) soils (Sebag et al., 2006a). Biostructured phytoclasts are described as originating from local vegetation (Tyson, 1995), but they can also be deposited in river channels during flooding (Batten, 1996). ...
... The amount of opaque phytoclasts gradually increases in aquatic environments, as they are deposited distally from source areas (Sebag et al., 2006a). Opaque phytoclasts are the most resistant components in the particulate organic matter and are usually linked to coarse sediments in high-energy environments (Oboh, 1992;Tyson, 1995). ...
Article
The aim of this paper is to reconstruct an 11,000-year history of depositional environmental change in southeastern Brazil, based upon the integration of particulate organic matter and stable isotope (C and N) data from a 136-cm sediment core from Lake Canto Grande. These proxies are used to explore the evolution of terrestrial and marine influence on the lake. Isotopic (δ¹³C: −27.87‰ to −31.9‰; δ¹⁵N: −0.07‰–4.9‰) and elemental (total organic carbon - TOC: 0.58%–37.19%; total nitrogen - TN: 0.08%–1.73%; C/N: 0.3 to 54.7) values recorded in Lake Canto Grande suggest that the sedimentary organic matter was derived from mostly C3 land plants and freshwater phytoplankton. Particulate organic matter and cluster analyses distinguished four associations characterized by the predominance of amorphous organic matter, followed by phytoclasts and palynomorphs. These results indicate two different phases of lake evolution. The first phase (136 - 65 cm; ∼10,943 cal yr. B.P. to ∼8529 cal yr. B.P.) is recorded by sand layers interbedded with mud, which contain amorphous organic matter (AOM, 45–59%) and phytoclasts (opaques - OP: 6–18%; non-opaques – NOP: 17–23%) which indicate a floodplain area. The second phase (65–0 cm; ∼8529 cal yr. B.P. to ∼662 cal yr. B.P.) comprises mud, AOM (68–86%) and palynomorphs (PAL, 8–16%) related to lake establishment comparable to modern conditions. Thus, characterizing particulate organic matter, in combination with stable isotopes, proved to be invaluable proxies for lacustrine paleoenvironmental change through the Holocene.
... 5 and 6). The low gelified phytoclast/ AOM ratios, and the low percentage of altered phytoclasts (Fig. 4), suggest pedogenetic input or sub-aqueous degradation, and a reduced fluvial influence, respectively (Sebag et al., 2006b;Sifeddine et al., 1995Sifeddine et al., , 1996. The presence of aerophilic and planktonic diatoms support this interpretation; whereas the high percentage of translucent phytoclasts, palynomorphs, and the presence of macrophytes could be related to autochthonous vegetation from proximal areas (e.g., Sebag et al., 2006b;Traverse, 2007). ...
... The low gelified phytoclast/ AOM ratios, and the low percentage of altered phytoclasts (Fig. 4), suggest pedogenetic input or sub-aqueous degradation, and a reduced fluvial influence, respectively (Sebag et al., 2006b;Sifeddine et al., 1995Sifeddine et al., , 1996. The presence of aerophilic and planktonic diatoms support this interpretation; whereas the high percentage of translucent phytoclasts, palynomorphs, and the presence of macrophytes could be related to autochthonous vegetation from proximal areas (e.g., Sebag et al., 2006b;Traverse, 2007). ...
... This marked fluvial influence would be responsible of the dilution of sporomorphs and the infilling of La Caimana valley at a rate that might be well in excess of our estimate of~600 cm/ka. The conspicuous increase in the gelified AOM suggests high degradation rates and aerobic diagenesis (Sebag et al., 2006b;Sifeddine et al., 1996). This, together with the diatom assemblage, suggests sub-aerial exposure. ...
Article
The detailed palynofacies analysis of the late Holocene laminated succession of the San Nicolás terrace in the middle Cauca Valley, northern Colombia, is interpreted as the product of sedimentation in a lacustrine to fluvial dominated setting. Radiocarbon analyses reveal that the succession was deposited between ~3500 and a few hundreds of years with sedimentary rates in excess of ~600cm/ka. The milimetric laminae and the high frequency fluctuations in the content of the palynodebris of terrestrial origin, i.e., the high altered ligno-cellulosic debris/amorphous organic matter ratio, together with diatoms typical of fluvial conditions, such as Aulacoseira granulata do suggest an intermittent and continuous hydrological and biological connectivity with the Cauca River, akin to a varzea lacustrine environment. Drier to wetter conditions appear to occur, moving upward in the succession. This might reflect regional precipitation conditions all along the Cauca Valley and the southern migration of the intertropical convergence zone.
... No entanto, as cutículas identificadas neste testemunho apresentam-se bem preservadas, refletindo que sua deposição deva ter ocorrido próxima a área fonte . Os fitoclastos não-opacos não-bioestruturados, identificados em alguns trabalhos (SEBAG et al., 2006a;2006b;BOUSSAFIR et al., 2012;ZOCATELLI et al., 2012) como partículas gelificadas, são partículas sem estruturas e de cor marrom, tendo sua origem relacionada a degradação de tecidos de plantas em ambientes aquáticos, tais como lagos, ou em condições anaeróbicas como em solos hidromórficos (SEBAG et al., 2006a). Além dos não-bioestruturados, os fitoclastos não-opacos bioestruturados listrados foram registrados como elementos subordinados nas palinofácies 1 e 2, que caracterizam a fase 1 na evolução da Lagoa Canto Grande. ...
... No entanto, as cutículas identificadas neste testemunho apresentam-se bem preservadas, refletindo que sua deposição deva ter ocorrido próxima a área fonte . Os fitoclastos não-opacos não-bioestruturados, identificados em alguns trabalhos (SEBAG et al., 2006a;2006b;BOUSSAFIR et al., 2012;ZOCATELLI et al., 2012) como partículas gelificadas, são partículas sem estruturas e de cor marrom, tendo sua origem relacionada a degradação de tecidos de plantas em ambientes aquáticos, tais como lagos, ou em condições anaeróbicas como em solos hidromórficos (SEBAG et al., 2006a). Além dos não-bioestruturados, os fitoclastos não-opacos bioestruturados listrados foram registrados como elementos subordinados nas palinofácies 1 e 2, que caracterizam a fase 1 na evolução da Lagoa Canto Grande. ...
... Em ambientes aquáticos, a quantidade de fitoclastos opacos gradualmente aumenta à medida que são depositados distalmente da área fonte, fato explicado devido ao aumento da alteração dos componentes terrestres durante o transporte (SEBAG et al., 2006a). Os fitoclastos opacos são os componentes mais refratários da matéria orgânica particulada e geralmente são associados a sedimentos de granulometria grossa em ambientes de alta energia (TYSON, 1995). ...
... • Aerobic degradation: Comprises all degradation signs that are connected to the presence of air, for example, mesofaunal droppings, fungal remains, including micro-fissured bones (after Babel, 1975;Craft, 2001;Huisman, 2009;Sebag et al., 2006;Turner-Walker & Jans, 2008). This group does not include aerobic organic degradation in oxygenated water (see Boyd & Tucker, 2012). ...
... This group does not include aerobic organic degradation in oxygenated water (see Boyd & Tucker, 2012). • Anaerobic degradation index: Degradation indicators that are connected to the presence of water/absence of air, such as gelified organic matter, including bones with cyanobacterial tunnelling (after Babel, 1975;Craft, 2001;Huisman, 2009;Sebag et al., 2006;Turner-Walker & Jans, 2008). ...
Article
Micromorphological analysis is used to improve our understanding of wetland site taphonomy and stratigraphy. Twelve profile columns from the Neolithic lakeshore site of Zug‐Riedmatt are macroscopically described here, microscopic analyses are applied to sediment facies, defining 14 sedimentary units (U): The natural basal sediment (U1) is carbonate‐rich, U2 a transition phase to the anthropogenic units U3 to U12. Uppermost are the natural carbonate‐rich U13 and U14. The creation of a micromorphological database and the application of 27 defined indices allow a better understanding of the natural, anthropogenic and taphonomic processes taking place at the site. Natural sediment input originated from Lake Zug, the nearby river Lorze with its delta, and a local marshy waterbody. Organic rich accumulations and calcitic ash played a major role in pH changes, leading to carbonate and silica dissolution, alongside bone alteration. Signs of degradation processes under aerobic and anaerobic conditions within a single layer points to complex, multiphase processes under changing water levels, a milieu belonging to both land and water, an amphibious environment. Finally, good layer preservation seemingly correlates to low aquatic reworking in a stable depositional context linked to the marshy area.
... Dopplerite, or waterhard, is paleyellowish brown to dark brown, translucent material, commonly crossed by cracks upon drying. It forms during early diagenesis of plant tissues in an anaerobic, subaquatic or waterlogged environment, as in peat and hydric soils (see Section 5) (Lewis, 1882;Babel, 1975;FitzPatrick, 1993;Koopman, 1988;Sebag et al., 2006;Feller et al., 2010;Ismail-Meyer et al., 2013;Ismail-Meyer, 2014). Further investigation regarding the formation of gelified organic matter and dopplerite is clearly needed. ...
... Understanding changes relative to anthropogenic activities and the effects of cultivation, erosion, sedimentation, ground raising, compaction, waste deposition and fire may require integrative approaches using micromorphology, macrobotanical analyses, palynology and palynofacies analyses, possibly supplemented by molluscs, insect and diatom analyses, to interpret the form and distribution of soil organic matter, as well as to understand natural and anthropogenic soil formation processes (Kooistra & Kooistra, 2003;Sebag et al., 2006;Kü hn et al., 2013). These plant and animal remains can be useful, for instance, in establishing the succession of changes in natural communities and understanding land-use changes. ...
... Standard chemical preparation included removal of the mineral fraction with HCl and HF and humified organic matter with KOH. This technique preserves pollen and other organic matter (OM) analysed as palynofacies with the methods of the organic matter petrography (Combaz, 1964;Caratini, 1994;Tyson, 1995;Batten, 1999;Sebag et al., 2006). Several categories of particulate OM can be distinguished according to their optical properties: amorphous OM with indistinct outlines, discrete elements (recognizable organs or organisms), and phytoclasts (constituents produced by plants or derived from their degradation). ...
... The palynofacies (after Combaz, 1964;Tyson, 1995) contains mainly agglomerates of structureless amorphous organic matter (AOM), with very few discrete elements or recognizable organs and organisms (phytoclasts, palynomorphs). This indicates intensive pedological degradation and/ or biological activity in a sub-aquatic environment (Sebag et al., 2006). Among the structured elements, opaque particles (OP) are dominant, corresponding partially with charcoal particles and organic remains, which have undergone thermal maturation after burial. ...
Article
The site complex Ounjougou on the Dogon Plateau (Mali) comprises sediments up to 100,000 years old with numerous Pleistocene and Holocene sequences. The site Ravin de la Mouche (11.4–10.2 ka) is of special archaeological significance because in its Early Holocene deposits, pottery sherds have been found which are among the oldest in Africa. For a better understanding of the environmental conditions which might have contributed to the innovation of pottery making, a multi-proxy approach was applied to the sediments of Ravin de la Mouche, including phytoliths, pollen, palynofacies, micromorphology and charcoal. The multi-proxy approach also allows reconstructing the complex taphonomy of the site.
... Origin and transfer of particulate organic matter in recent environments. Sebag et al. (2006b) Holocene alluvial deposits from Lower Seine Valley. France. ...
... However, vegetation, water and oxygen supply (Eh-conditions) are considered most important factors for the generation of coal facies together with pH value and subsidence. Therefore, studies of modern peat derived from different types of vegetation growing in different hydrological environments have been proven to be very useful in interpreting coal facies (e.g., Cohen and Bailey, 1997;Cohen and Stack, 1996;Esterle and Ferm 1994;Hawke et al., 1999;Petersen and Nielsen, 1995;Roberts and McCabe, 1992;Sebag et al., 2006b;Staub, 1991;. Preservation and gelification of tissues, type and percentage of liptinite, and the nature and amount of mineral matter, as determined by petrographic analyses (Fig. 3), are some of the criteria used to approach conditions existing during the growth of peat-forming mires (Taylor et al., 1998;Teichmüller, 1989). ...
Article
Organic petrology developed as coal petrology at the beginning of the 20th century dedicated mainly to the study of coals because of their utilization in industry. Coal petrology was then considered a branch of coal science. Later, with the development of specialized nomenclature, classification of coal components, and the standardization and improvement of analytical (microscopical) methods, this discipline expanded in interests and name, becoming organic petrology. Organic petrology carries a broader context, being as well a tool applied in the study of dispersed organic matter in sedimentary rocks due to its importance in exploration for fossil fuel resources. At present, organic petrology is a discipline widely recognized for its role in fundamental and applied research with respect to both coal utilization and in geosciences. Throughout the 20th century several important monographs have been published on the discipline of organic petrology, including “Stach's textbook of coal petrology” (1st edition 1935, 2nd 1975, 3rd 1982), updated as the more general “Organic petrology” by Taylor et al. (1998). More recently, the text “Applied coal petrology: the role of petrology in coal utilization” was published by Suárez-Ruiz and Crelling (2008). This review is the first in a two-part review series that describes and updates the role of organic petrology in geosciences. A second part complementing this one and focused on the applications of organic petrology to other scientific fields will follow.
... The rate of peat subsidence should also be taken into account. Studies of modern peat vegetation in a variety of hydrological and climatic environments have facilitated the analysis of Carbonaceous facies (e.g., Cohen and Bailey, 1997;Cohen and Stack, 1996;Esterle and Ferm, 1994;Hawke et al., 1999;Petersen and Nielsen, 1995;Roberts and McCabe, 1992;Sebag et al., 2006;Staub, 1991;Wüst and Bustin, 2001). Some criteria used to determine the approximate conditions of peat genesis according to Taylor et al. (1998) and Teichmüller (1989) are the degree of gelification and preservation of plant tissues and the liptinite and mineral matter content in the tested coal. ...
Article
This paper presents the first attempt to develop the facies model of the entire coal deposit belonging to the Carboniferous productive sequence located in the western part of the Upper Silesian Coal Basin. To achieve this objective, six seams from the Knurów deposit were examined. The deposit belongs to the largest producer of coking coal in Europe, which is Jastrzębska Spółka Węglowa SA (Polish state-run coking coal producer). The maceral composition, vitrinite reflectance, ash yield content, moisture content, gross calorific value, and volatile matter yield were determined. Coals from the Knurów deposit are classified as ortho-bituminous and meta-bituminous coals. Their average degree of coalification, determined by vitrinite reflectance, is RO = 0.79% to RO = 1.09%. Petrographic indices and the analysis of facies diagrams were used to develop the facies model. It was shown that the facies development and sedimentological evolution of the Knurów deposit were determined by the river system extended to the upper delta plain. In accordance with the stratigraphic succession, the oldest deposits are dominated by the reed facies (mainly Calamites) growing in oxbow lakes and dry streambeds. With the passage of time, the importance of the river system for the development of the paleo-environment decreased. Transitional bogs with mixed plant communities were formed. This started the conversion of wetlands into areas occupied by wet forest. At the end of the sedimentation of the documented coal seams in the Knurów deposit, lowland bogs (fens), which were subject to frequent fires, dominated the landscape. Based on a detailed maceral analysis and facies diagram analysis, a strong correlation between fault occurrence and coal facies developed under paleo-river influence was displayed. The aim of the study is to show environmental changes during deposit formation in the context of geological exploration.
... This optical method consists of the study of thin slides of a total assemblage of particulate OM previously isolated from sedimentary rocks using acid digestions (HCl/HF). Initially developed by Combaz (1964), this technique is frequently used for the characterization of particulate OM in lacustrine sediments (e.g., Jacob et al., 2004; Noël et al., 2001; Sifeddine et al., 1995) and in soils (e.g., Graz et al., 2010; Sebag et al., 2006b,c). This approach involves the characterization of different organic constituents showing a large diversity in terms of size, texture, color, opacity and recognizable biological structures (cf. ...
... 1fig. 1) : 1) le plateau calcaire et sa couverture en altérites (argiles à silex, ou altérites à silex, ou rS), dépôts sablo-argileux résiduels (limon de plateau ; Laignel, 1999Laignel, , 2002a) ; 2) les versants avec les dépôts de solifluxion (biefs à silex ; Laignel, 2002b) ; 3) le fleuve Seine et ses affluents qui stockent des dépôts alluviaux (les limons et les dépôts tour- beux ; Sebag, 2002 ; Laignel, 2003). À partir des années 1960, plusieurs sites de la basse vallée de la Seine ont été étudiés (fig. 1) : la baie de Seine (Garnaud, 2003), l'estuaire de la Seine (Delsinne, 2005 ; Sorrel, 2009), le Marais vernier (elhaï, 1959 ; Huault, 1980 Huault, , 1983 Huault, , 1985 Frouin, 2006 Frouin, , 2007a Frouin, , 2007b Frouin, , 2009 ), la tourbière d'Heurteauville (Huault, 1986 ) et le méandre de Berville sur Seine (Sebag, 2002Sebag, , 2006aSebag, , 2006b), 1980, 1983 Frouin, 2007 Frouin, , 2009, 2009, 2007a, 2007b Huault, 1980 Huault, , 1983 Sebag, 2002 ; SRA, donnés non publiées). ...
Article
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Les changements climatiques post-glaciaires et les fluctuations du niveau de la mer, ont fortement conditionné les environnements et la sédimentation du nord-ouest de l'Europe. À ces facteurs naturels, s'ajoute la croissance de la pression anthropique. Le défrichement forestier et le développement des pratiques agricoles sont les principaux facteurs étant à l'origine des processus érosifs dans le nord-ouest de l'Europe. Cet article a comme finalité principale l'analyse des séquences holocènes dans la basse vallée de la Seine et ses affluents, de comprendre l'origine des apports détritiques et terrigènes ainsi que la part relative de l'activité humaine. Une première étape de cette étude porte sur l'analyse de secteurs principaux de la basse vallée de la Seine : la zone estuarienne, la zone fluviale et la zone des affluents. Ces secteurs sont caractérisés par un contraste sédimentaire. A partir de la description de chaque zone, on montrera quelles sont les phases érosives majeures à l'origine des épisodes détritiques importants. Detritus sedimentation in the lower Seine valley over recent millennia Post-glacial climate change and fluctuations in sea level had a significant impact on environments and sedimentation in NorthWest Europe. In addition to these natural factors, growing anthropic pressure also had an effect. Forest clearing and the development of agriculture were the main factors behind erosion processes in NorthWest Europe. This article aims to analyse Holocene sequences in the lower Seine valley and its tributaries, in order to understand the origins of soil and detritus sediments, including those related to human activity. The first step of this study is based on the analysis of the lower Seine valley's main regions: the estuary zone, the fluvial zone and the tributary zone. These areas are characterised by sediment contrast. The major erosion phases behind episodes of significant detritus sedimentation are described for each zone.
... This optical method consists of the study of thin slides of a total assemblage of particulate OM previously isolated from sedimentary rocks using acid digestions (HCl/HF). Initially developed by Combaz (1964), this technique is frequently used for the characterization of particulate OM in lacustrine sediments (e.g., Jacob et al., 2004; Noël et al., 2001; Sifeddine et al., 1995) and in soils (e.g., Graz et al., 2010; Sebag et al., 2006b,c). This approach involves the characterization of different organic constituents showing a large diversity in terms of size, texture, color, opacity and recognizable biological structures (cf. ...
... The characterization of currently existing peaty areas is established according to the nature of the water resources, the origin and nature 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. ...
Article
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 10586 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 environments such as coal deposits associated with fluvial paleoenvironments.
... Microscopic organic matter particles preserved in lake sediments have been studied intensively during the last few decades in connection with hydrocarbon exploration (Tyson 1995;Batten 1996Batten , 1999Mendonça Filho et al. 2012), paleoclimate inferences (Bombardiere and Gorin 1998;Pellaton and Gorin 2005), paleoenvironmental and paleoceanographic reconstructions (Batten 1982(Batten , 1996Tyson 1995;Williams et al. 1995;Tyson and Follows 2000;Tribovillard et al. 2001) and biostratigraphic correlation (Batten 1996;Tyson 1995;Batten and Stead 2005;Blandon et al. 2008). Palynofacies analysis is used to distinguish among lacustrine (Di-Giovanni et al. 2000), palustrine (Laggoun-Défarge et al. 1995) and paludal environments (Bourdon et al. 2000;Sebag et al. 2006a), and to evaluate synsedimentary, early diagenetic and pedogenic processes (Di-Giovanni et al. 1999;Bourdon et al. 2000). Combaz (1964Combaz ( , 1980 first defined palynofacies as the microscopic organic matter of rocks or unconsolidated sediments that is resistant to inorganic acids. ...
Article
We conducted a palynofacies analysis on late Holocene fluvio-palustrine sediments from a succession that outcrops as a terrace proximal to the Cauca River, Colombia, in northern South America. The succession is composed of laminated clay, organic-rich laminae, sand beds and buried soils. These buried soils range in thickness from 2 to 16 cm and are composed of silty clay with varying degrees of root bioturbation and have a gray-green-bluish color. They could classify as Entisols and in this article we refer to them as paleosols. Samples from each of these sediment types (except sand), and samples from two modern-analog environments, also on the proximal part of the Cauca River, i.e. sediment from a seasonally flooded pond and the upper-most layer of a modern soil, were analyzed for organic matter content. Prior to selection of an organic matter extraction method, four protocols were tested on the modern pond sediment sample. A modified protocol involving flotation with ZnCl2 proved to be the best method for these sediment types. We produced an atlas of the main taxa and their relative proportions found in this study and propose this method as an excellent approach to environmental reconstruction of fluvial environments. Very little work has been done on fluvio-palustrine palynofacies in the Neotropics.
... By applying the microscopic grid method and with reference to the system of Troels-Smith (1955), the groups of biocomponents in peat and lake sedi- ments (Tobolski 2000) and the classification used in the palynofacial analysis of the sediments from the valley of the Seine River ( Sebag et al. 2006), the following forms of organic matter were recognized: 1. Amorphous organic matter (Fig. 5A): crumbled amorphous material of vague outline and oblit- erated cellular structure. Thanks to its intense, dark colour the matter can be distinguished from grey or yellowish-grey components of min- eral or mineral-organic origin. ...
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Distinction between organic components accumulated in situ and those deposited by sedimentation is essential for the assessment of the intensity and extent of impact of geomorphological processes. Authigenic components include moss remains, fragments of the root systems of herbaceous plants and trees, the epidermis of rhizomes, and leaf sheaths, as well as a fungal mycelium. Among the allogenic components are aboveground parts of plants, including leaves of vascular plants, wood, epidermis and periderm, sporomorphs, sporangia, fruits and seeds, as well as zooclasts and protist remains. Microscopic grid analysis allows the share of individual morphological forms of organic matter to be determined in order to reconstruct the deposition conditions on the floodplain. This method makes it possible to detect episodes of activity of fluvial, aeolian and slope processes even when not accompanied by sedimentation of mineralogenic components.
... because variations of relative abundances were also lower than 5% (Sebag et al, 2006a,b). ...
Article
Classical palynofacies method, which consists in an organic concentrate microscopic qualitative observation after mineral phase dissolution, is commonly used in order to study sedimentary organic matter. In the present study we develop a new quantitative palynofacies method that allows organic particles mass concentrations to be determined in studied samples. This method was developed to help quantify the input of fossil organic matter (FOM) into modern environments as a result of sedimentary rocks weathering. Studied samples were collected from different pools, like bedrocks, weathering profiles, soils and riverine particles in an experimental watershed “Le Laval”. This watershed overlying Callovo-Oxfordian marls (1 km² in area) is located near Digne, Alpes-de-Haute-Provence, in France. In addition to palynofacies techniques, Rock-Eval 6 pyrolysis and Al2O3 content measurements (inductively coupled plasma emission spectrometry) were carried out on the samples. Obtained results show that this quantitative palynofacies method is suitable for FOM studies in modern environments, and FOM particles are quantified in the different pools. Results also give evidence that FOM alteration depends on the type of weathering, but also on the kind of organic particles. Soil formation under vegetation, resulting from the (bio)chemical weathering, lead to fossil organic particles concentration losses that do not exceed 30%. Elsewhere, mechanical weathering appears extremely fast and has no qualitative or quantitative influence on the observed FOM particles, which feeds directly into riverine stocks. FOM appears to be very resistant to weathering processes, this highlights its occurrence into supergene pools and then into carbon cycle. Quantitative palynofacies analysis is a new method adapted to a such study, but can also be applied to other palynological, paleoenvironmental or archeological studies.
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The Northern coastline, from Kayar to Saint Louis (Senegal) is characterized by a succession of dunes and inter-dunes. Coastal wetlands located in the inter-dunes which bear Organic Matter (OM) rich soil where market garden agriculture is the main activity. These zones locally called “Niayes” are characterized by shallow groundwater table threatened by anthropogenic pressure, climate and environmental impacts. The scientific interest of this research work is to characterize the composition of soil OM to discuss its origin, composition, and diagenetic evolution in this depositional environment of Mboro research site with regard to natural and anthropogenic pressure. Three selected core samples with depth interval of 5 cm aligned in along a slope transect in the Mboro wetland were carried out. Soil OM were analyzed for Particulate OM, C/N, Rock-Eval HI and OI, δ¹³C, δ¹⁵N whereas sediments and water were respectively analyzed for grain size distribution, water contents and redox potential down to 50 cm depth. We have demonstrated through the results a vertical variability in the content, the nature and preservation quality of sedimentary OM with the occurrence of a peat storage zone. The isotopic markers depict a strong contribution of C3 plants, macrophytes and to a lesser extent of algae and microbial organic materials. High concentrations of dissolved nutrients occurring mainly on the surface slope may derive from the use of fertilizers to improve agricultural yields. These results constitute an added value in the scientific knowledge of this sector of the Niaye of Senegal.
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Despite a first study dating from 1986 (Richardson, 1986), magnetic mineralogy in peat was not considered and used as a potential palaeoenvironmental proxy until very recently. The first aim of our study was to determine what technics can be used on peat (SIRM, SARM and their demagnetization) and how, to overcome the specific problems arising from the use of peat : very low magnetic signal, evolution of the signal through time, etc. The relevant magnetic procedure was then applied to three peat cores frome La Trézence peat bog(Charente-Maritime, France) along with geochemical analyses giving informations on the environmental evolution throught time. After comparison of all the results, part of the magnetic mineralogy variations fits with environmental evolution. The other part can be concidered as a proxy of pedologic processes that studied geochemical parameters do not show.
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Le remplissage sédimentaire des mares de Bangou-Bi et de Tankalawal (SW Niger) a fait l’objet d’une étude de son contenu organique qui fournit des informations sur l’origine et les conditions de dépôt du matériel sédimentaire. Deux carottes mesurant respectivement 140 cm (carotte BB2) et 60 cm (carotte TK1) ont été étudiées. Les échantillons ont été soumis à une pyrolyse Rock-Eval 6 renseignant sur la géochimie globale de la Matière Organique (MO) et le signal S2 de la pyrolyse a été exploité afin de mieux préciser la nature de ces MO. Le niveau argilo-limoneux de la carotte BB2 contient une MO aquatique et terrestre dont la composition en composés hydrocarbonés se répartit entre les biopolymères (F1+F2), et les géopolymères matures (F3) et immatures (F4). Cette MO serait déposée dans un environnement calme. En revanche le niveau inférieur sableux renferme une MO terrestre très altérée et enrichie en géopolymères matures qui serait amenée par des pulses détritiques grossiers (colluvionnement) issus du bassin versant. Les valeurs des paramètres géochimiques et leur évolution avec la profondeur indiquent que la MO de la carotte TK1 est aquatique et a enregistré une dégradation en milieu anoxique. Cette MO contenant majoritairement des géopolymères matures (F4) riches en lipides se révèle étonnamment plus résistante face à l'altération que celle présente dans la carotte BB2.
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Post-glacial climate changes and sea-level fluctuations have strongly influenced N-W European environments and sedimentation. To these natural events, increasing anthropogenic pressure has to be added. Forest clearance and agricultural development are the main factors responsible for the erosional processes in Northwest Europe. This article analyses Holocene sequences of the Lower Seine Valley (LSV) (Paris Basin) to understand better the origin of detrital and terrigenous input and how much humans have contributed to it. Three main sectors of the LSV are analysed: estuarine, fluvial and tributaries. Since Neolithic times, there are seven erosional phases that can be identified and essentially linked to human pressure. Terra Nova, 00, 000–000, 2010
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A multidisciplinary study has been carried out on the Late Miocene (Messinian) Calcare di Base Formation in northern Calabria, Italy, with the aim of understanding the depositional conditions of these enigmatic carbonate sediments that have been interpreted as evaporitic or diagenetic limestone. The research has been developed through sedimentological (microfacies), organic petrography and geochemical analyses (palynofacies, Rock-Eval pyrolysis and gas chromatography/mass spectrometry). The carbonates studied preserve their original mineralogy (aragonite) and microstructure.
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Samples of Albian Tégulines Clay outcropping near Brienne-le-Château in the eastern part of the Paris Basin were subjected to a geochemical characterization of organic matter (OM), combining OM bulk Rock-Eval analysis (RE), organic petrography and molecular analysis. In this study, the objective was to investigate the oxidation of natural organic matter in critical zone developed in early reduced marine clay formation. For that purpose, core samples from three boreholes crosscutting the Tégulines Clay formation down to the Greensands were selected. Several meters of Brienne marls preserved Tégulines Clay from atmosphere and therefore from high weathering and high oxidation in AUB240 borehole, whereas Tégulines Clay were weathered in their upper part in AUB1010 and in AUB230 boreholes as a result to their vicinity to the surface. The results showed that the Total Organic Carbon (TOC) contents in all clays are very low, ranging between 0.3 and 0.7 wt%. The RE bulk data and Tmax parameter of OM in preserved Tégulines Clay indicate that the OM is immature. The organic petrography shows a predominance of gel-like amorphous OM preserved by natural sulphurisation in anoxic environments. Organic matter in Tégulines Clay from the AUB230 and AUB1010 boreholes show similar characteristics. The OM at the top of Tégulines Clay contains large amounts of oxidized lignocellulosic debris and has high RE Oxygen-Index values. In the first upper 10 m of the clays, the RE bulk, organic petrography and molecular data revealed oxidative events (high OI and high oxidized debris contents). Below 10 m, the OM is almost preserved. The OM in the reduced marine Tégulines Clay formation is very little functionalized and seems to be slightly reactive but not negligibly with the inorganic fractions in presence of oxygen.
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The Upper Doubs River Valley is a 910-km2watershed feeding into Lake Chaillexon. The lake was formed by a natural rockfall at the end of the Bølling Chronozone (around 14,250 cal yr B.P.) and since then has trapped material eroded from the watershed. The filling process and variations in sediment yield have been investigated by mechanical coring, seismic surveys, and electric soundings. The detrital sediment yield of the upstream watershed can be calculated by quantifying the sedimentary stocks for each climatic stage of the Late-Glacial period and Holocene Epoch and estimating the lake's entrapment capacity. This enables us to determine the intensity of the erosion processes in relation to climate and environmental factors. The Bølling–Allerød Interstade produced the greatest yields with mean values of 19,500 metric tons per calendar year (t/yr). The Younger Dryas Chronozone saw a sharp fall (8900 t/yr) that continued into the Preboreal (2100 t/yr). Clastic supply increased during the Boreal (4500 t/yr) before declining again in the Early Atlantic (2400 t/yr). Since then, yields have risen from 4500 t/yr in the Late Atlantic to 6800 t/yr in the Subboreal and 11,100 t/yr in the Subatlantic. Comparison of quantitative data with the qualitative analysis of the deposits and with the paleohydrologic curve of the watershed based on level fluctuations in lakes around Chaillexon shows that climate was the controlling factor of sediment yield until the Late Atlantic. From the Late Atlantic–Subboreal around 5400 cal yr B.P. (470014C yr B.P.) and especially from the end of the Subboreal Chronozone and during the Subatlantic Chronozone (2770 cal yr B.P./270014C yr B.P.–present) climatic constraints have been compounded by human activity related to forest clearing and land use.
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The particulate organic matter isolated from soils and from underlying geologic formations from Various french watersheds was studied under the light microscope to determine palynofacies composition. The results reveal that modern humus contain notable amounts of ancient organic constituents inherited from the geologic substratum. This ancient contribution varies both qualitatively and quantitatively, mainly as function of the substratum composition. This implies that the cartography of surface formations and the knowledge of their composition is a prerequisite to the evaluation of the soil organic carbon reservoir and to the determination of its turnover. A more immediate conclusion is to remind us that the coaly debris that occur naturally in soils does not always derive from modern biologic production and from pollution.
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Boreal and subarctic peatlands comprise a carbon pool of 455 Pg that has accumulated during the postglacial period at an average net rate of 0.096 Pg/yr (1 Pg = 10(15) g). Using Clymo's (1984) model, the current rate is estimated at 0.076 Pg/yr. Long-term drainage of these peatlands is estimated to be causing the oxidation to CO2 of a little more than 0.0085 Pg/yr, with combustion of fuel peat adding almost-equal-to 0.026 Pg/yr. Emissions of CH4 are estimated to release almost-equal-to 0.046 Pg of carbon annually. Uncertainties beset estimates of both stocks and fluxes, particularly with regard to Soviet peatlands. The influence of water table alterations upon fluxes of both CO2 and CH4 is in great need of investigation over a wide range of peatland environments, especially in regions where permafrost melting, thermokarst erosion, and the development of thaw lakes are likely results of climatic warming. The role of fire in the carbon cycle of peatlands also deserves increased attention. Finally, satellite-monitoring of the abundance of open water in the peatlands of the West Siberian Plain and the Hudson/James Bay Lowland is suggested as a likely method of detecting early effects of climatic warming upon boreal and subarctic peatlands.
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Sedimentary organic matter has been systematically studied in an eight-metre long core from the centre of the Petit Lac (Annecy, French Alps). The palynofacies composition identifies different terrestrial organic sources including forest floors, soil-horizons and geological substratum. The amount of recycled organic matter derived from the geological substratum is estimated and subtracted from the other contributions from the catchment area. The palynological record indicates that the relative variations in organic sources are directly dependent on human land-use. From ca. 5000 to 1700 BP, the human impact on soil cohesion is very low and organic matter is mainly exported from the surficial forest floor. The Roman invasion (ca. 1700 BP) marks the most important ecological and hydrological change. From 1700 to 900 BP, the clearing of forests released deeper-soil components. This trend is increased after 900 BP with agriculture intensification, which resulted in a higher sedimentation rate. In all the periods, extreme events such as flood or intensive run-off are characterised by notable increases of organic matter from surface (5000 to 1700 BP) and deep (1700 BP to now) soils.
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For over a century the Seine estuary has been highly affected by human activities, resulting in a reduction of the surface of wetland habitat. Several ponds of the Vernier Marsh, one of the main wetlands of the estuary, are being filled in by sediment. The St. Aubin canal, the only inlet from the Seine to the wetland, has regularly been opened in summer to maintain a sufficiently high water level in the system. The purpose of this study was to identify the origin of filling: natural evolution of eutrophication or human intervention by the opening of the St. Aubin canal? Sediment cores were sampled at 19 stations randomly distributed in the ponds of the wetland. Granulometric, micro-granulometric and geochemical analyses (ignition loss, C/N/P, chemical fractionation of particulate phosphate) were performed on the top 10 cm of sediment. Moreover nutrient concentrations (ammonium and phosphate) were measured in the interstitial waters using diffusion samplers. The results revealed that sediments sampled from the north are weakly organic (ignition loss: 19%, 15% C, 0.9% N , 40% organic P of total P) whereas those sampled from the southern stations are highly organic (ignition loss: 50–93%, 35% C, 1% N: 59–81% organic P of total P). In summary, sediments accumulating in the north of the ecosystem mainly consist of minerogenic particles from the Seine transported by the St. Aubin canal and thus are a result of the human interference. Interestingly the accumulation of sediments in the southern part is the result of a natural evolution of eutrophication: a peat bog. These sediments are highly organic, enriched with organic particulate phosphate, specifically a humic-acid-bound-phosphorus, a refractory form of phosphorus.
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If in a virgin peatland the carbon input from the atmosphere (always as CO2) equals the output, about 25% or less of the carbon may be released in the form of CH4. A climatic shift to higher temperatures will increase the release of CH4 from deep peat deposits, particularly from tundra soils. Likewise, the release of CO2 will increase, but hardly by more than 25% of its present level. -from Author
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Optical analysis (palynofacies) of the organic matter (OM), occurring in various compartments (soils, bedrock formations, lacustrine chalks) of the lacustrine basin of Chaillexon (Doubs, France) has led to the definition of organic markers. Their variable contributions were observed in suspended matters taken over a period of a year (annual scale) and in lacustrine sediments covering the last 12,000 years B.P. (millennial scale). Results obtained lead to three main conclusions. Firstly, there exists a seasonal variation in the detrital organic fluxes, directly linked to the autumnal litter production. This allows us to distinct the detrital OM loaded during autumn-winter organic floods and spring-summer ones. Secondly, the organic record in Boreal to modern sediments of the lake of Chaillexon, fed by autumn-winter fluxes, appears mainly controlled by the autumnal productivity of vegetal biomass. Thirdly, the organic record does not point out a progressive evolution of organic fluxes linked with successive climatic phases. It shows abrupt ruptures of the balance (threshold effects) corresponding with the passage of the tree line in the watershed. These ruptures are not necessarily synchronous with climatic fluctuations.
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The petroleum quality (IH) of the humic organic matter of the Mahakam delta is very variable at given total organic carbon and maturation index. The HI is not only correlated to the organic composition, but also to the mutual spatial relations of the organic and mineral constituents. A characteristic organo-mineral microtexture has been identified in each depositional environment of this delta. There is an abridged English version. -English summary
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The petrographical study of the sedimentary organic matter contained in recent sediments from "Le Petit Lac d'Annecy" allows to obtain a palaeoenvironmental signal based on the autochthonous/allochthonous organic matter ratio of the past 1000 years. The new limnological regime, linked with the anthropisation of the watershed, makes possible to read directly this signal in terms of lacustrine phytoplanktonic production since ca AD 1000. This signal also points out various erosion events seen by specific organic deliveries from the watershed, evidencing periods of increased running-off or intensive land-uses.
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The petrographical and geochemical study of superficial peat and living higher plants of Tritrivakely peaty marsh (Madagascar) has enabled the determination of (1) origin of peat organic matter, (2) some parameters which account for variations in depositional conditions, especially water table level, and their effects on organic matter preservation of accumulated peat. Moreover, transmission electron microscopy on ultrathin sections histochemically stained for phenols and polysaccharides revealed the distribution of these components in plant tissues and amorphous organic matter, and enabled their evolution during early diagenesis to be followed. It appears that the phenolic parts are nanoscopically amorphous, while polysaccharidic laminae are bioresistant, and probably belong to plant cell walls.
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A sedimentological study of a 755 cm length core sampled in the marshy depression surrounded by a cloud forest in the central Andes reveals that this site has recorded important environmental variations during the last 50 000 years. For the most part (625 cm) the core is composed of detrital rich sediments deposited during the Upper Pleistocene. The highest amount of detrital influx underlines the Last Glacial Maximum which ranges from ca 29 000 14C yr B.P. to ca 16 000 14C yr B.P. (ca 18 500 cal yr B.P.), between two relatively humid phases. The sedimentation of the present Interglacial, starting at ca 12 500 14C yr B.P. (14 500 cal yr B.P.), is mainly organic, as a consequence of the great development of soils and the forest vegetal cover all over the catchment area. The maximum extension of this vegetal cover ranging from 12 500 to ca 10 500 14C yr B.P. (14 500 and 12 400 cal yr B.P.) is followed from 10 500 to 8000 14C yr B.P. (12 400 and 8800 cal yr B.P.) by a drier period as revealed by the occurrence of micro-charcoals in the sediment. Between ca 8000 and 4000 14C yr B.P. (8800 and 4500 cal yr B.P.), the sharp increase of micro-charcoals content, likely related to palaeofires, underlines an intensification of this dry trend.
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Optical analysis (palynofacies) of the organic matter (OM), occurring in various compartments (soils, bedrock formations, lacustrine chalks) of the lacustrine basin of Chaillexon (Doubs, France) has led to the definition of organic markers. Their variable contributions were observed in suspended matters taken over a period of a year (annual scale) and in lacustrine sediments covering the last 12,000 years B.P. (millennial scale). Results obtained lead to three main conclusions. Firstly, there exists a seasonal variation in the detrital organic fluxes, directly linked to the autumnal litter production. This allows us to distinct the detrital OM loaded during autumn-winter organic floods and spring-summer ones. Secondly, the organic record in Boreal to modern sediments of the lake of Chaillexon, fed by autumn-winter fluxes, appears mainly controlled by the autumnal productivity of vegetal biomass. Thirdly, the organic record does not point out a progressive evolution of organic fluxes linked with successive climatic phases. It shows abrupt ruptures of the balance (threshold effects) corresponding with the passage of the tree line in the watershed. These ruptures are not necessarily synchronous with climatic fluctuations.
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Matter fluxes result from chemical and mechanical weathering that vary as a function of climate, relief, lithology and human activities. The aim of this paper is to characterize chemical weathering variations in the past using coaly particles found in both the geological substratum and the Holocene lacustrine sediments of a calcareous basin (Chaillexon lake, Doubs, France). Results point out that chemical weathering was the predominant erosional process in the watershed, which may be due to the calcareous nature of the bedrock. The significant variability of this process relative to mechanical weathering during the Holocene period can be interpreted as a consequence of the development of the vegetal cover induced by climate changes and human activity (forest clearing and landuse). Results also suggest that there is no direct relationship between chemical weathering in the watershed and autochthonous carbonate precipitation in the lake.
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The relationships between organo-mineral composition and early diagenetic processes in surface (< 50 cm) sediments from the Lac du Bouchet (Haute Loire, France) are presented. Parallel pore-water studies reveal downcore increases in dissolved organic carbon, inorganic carbon and CH4, illustrating the dominant methanogenetic degradation, but also highlighting regions of enhanced degradation due to sulphate reduction (confirmed by solid phase sulphur and pyrite distributions). Three sedimentary facies are observed: IA (0–25 cm) where the majority of compaction and degradation of the organic matter by diagenesis occurs in the absence of any significant change in the type of organic material or sedimentation rate; IB (25–40 cm) characterised by an increased grain size and diatom abundance; II (below 40 cm), whose base dates at 2500 ± 350 BP (i.e. within the Sub-Atlantic) shows high organic carbon contents and large grain size.
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Organic matter constitutes a minor fraction of marine and freshwater sediments, yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments. The organic matter content of sediments is the residue of past biota. The amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times. General sources of the organic matter are inferred from bulk properties such as elemental compositions, carbon and nitrogen stable isotope ratios, Rock-Eval pyrolysis data, and organic petrography. Details of organic matter origins are refined by analyses of biomarker molecular compositions. Source changes are proxies for fluctuations in sea-level, oceanic surface currents, and continental climates. Algal paleoproductivity rates are indicated by organic-carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions. These parameters record past availability of nutrients and, therefore, are proxies of surface mixing in the oceans and amount of land runoff to lakes. Sea-surface paleotemperatures are recorded by the number of carbon–carbon double bonds in lipid biomarkers produced by marine algae. Larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling. The δ13C and δD values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture, respectively. Diagenesis, which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials, can bias organic geochemical paleoenvironmental records. The magnitude of this potential source of misinformation must always be considered and evaluated. Comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change.
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Wetland peat deposits can be excellent archives of past changes in the depositional and ecological conditions under which they formed. Part of the story of these changes can be obtained from analysis of the palynomorphs preserved in these deposits; however, a more meaningful reconstruction can be achieved by combining organic petrography with palynology. An example of this approach is presented from a study of three sites in the northern Everglades of Florida. The primary purpose of this study was to test these combined methods for their utility in distinguishing between long-term, natural successions and recent, anthropogenically-derived disruptions of the ecosystem (such as diversions of drainage and introductions of contaminants from human sources). The combined palyno-petrographic method (supported by and dating) was able to establish with some certainty the first appearance of contaminant-driven plant types (such as cattails and duckweeds) into the region, with the organic petrography being more accurate in determining the actual presence of invading plants at a particular site and the palynologic analysis providing a broader picture of regional changes in the ecosystem (such as the direction of the plant invasion). The distribution of petrographic pyrite in these freshwater peats provided an additional new piece of evidence for contamination from the agricultural lands and also supported other evidence relative to the direction of contaminant infusion into the region. Additionally, the occurrence of significant quantities of pyrite at all three sites suggests that, in fact, none of these sites can be said to be totally unaffected by anthropogenic contamination. Longer hydroperiods were generally indicated by both methods for all sites before the early 1900s, confirming persistently wetter conditions in the Everglades prior to manmade changes in drainage. More specific paleohydrologic conditions could also be elucidated by this combined method, with all three sites displaying significant differences in hydrologic histories. Additionally, one of the sites is hypothesized to have been, until recently, in the center of a surface–water flow pathway, as indicated by the continuous presence at this site of deeper water aquatics (such as water lilies) and the smaller number of zones containing algal-derived carbonates and/or other petrographic indicators of oxidation or bioturbation.
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Quantified analyses of plant macrofossil remains have been made from three profiles of peat from raised bogs spanning a distance of 425 km from western Ireland to northern England. The reconstructed vegetation of each profile is related to changing bog surface wetness (BSW), and since the bogs are ombrotrophic these BSW changes are interpreted in terms of changing climate. Using age/depth models based on a total of 49 radiocarbon dates a number of wetter and drier phases are identified, and phase-shifts to wetter and/or cooler climates are defined. Prominent coincident changes to wetter conditions are dated in at least two of the profiles to ca 4400–4000, 1750, 1400, and 1000 cal. BP and in all three profiles at 3200, 2750–2350, 2250, and around 700 cal. BP. These phases are related to proxy climate changes in other terrestrial data sets from northwest Europe and a broad degree of synchroneity is demonstrated.
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The aim of this paper is to propose an initial estimation of the annual organic matter yield induced by chemical weathering of carbonates and shales, considering their global surface at outcrop and their organic matter content. The calculation also uses data on river fluxes resulting from carbonate rocks and shales weathering in major world watersheds, published by numerous authors. The results obtained from the studied watersheds have then been extrapolated to a global scale.Despite rather large uncertainty to such an approach, the calculated value of ca. 0.1 Gt implies that the annual organic carbon yield related to carbonates and shales chemical weathering might be a non-negligible component of the global carbon cycle. The individual contributions of different watersheds necessarily depend on the organic matter content of altered rocks. They are also obviously controlled by climatic parameters.The calculated yields do not constitute a direct supply to soils and rivers because of mineralisation when organic carbon is brought in contact with the atmosphere. Even so, the release of fossil organic matter would have implications for the global carbon cycle through the efficiency of the global chemical weathering as a carbon sink. Whatever the chosen hypothesis, the results of this study suggest that the recycled organic yield is a neglected component in the global organic carbon cycle assessment. Because it exists and, in addition, because it might represent a non-negligible carbon pool, fossil organic carbon deserves to be taken into account for a better evaluation of the organic stocks in soils and rivers presently only based on climatic data and current vegetal production.
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To assess the influence of climatic changes on organic lacustrine sedimentation, two cores recovered from the centre of the Lac du Bouchet were studied by petrographical (palynofacies) and geochemical methods. Only core LDB H was used for estimation of the organic fluxes. The variation of these fluxes with climo-stratigraphic periods showed: low organic fluxes during the Lateglacial, an increase at the beginning of the Holocene, a minimum at the end of the Atlantic period resulting from the climatic cooling, and a maximum at the end of the Sub-Boreal related to the installation of the present climatic conditions.
Article
A wide range of local, state, federal, and private programs are available to support the national (USA) policy of wetland ‘No Net Loss’. Implementation of programs, however, has resulted in the continued loss of natural wetlands on the premise that restored or created wetlands will replace the functions and values lost by destruction of natural wetlands. What are the ecological implications and consequences of these programs from a biodiversity and ecosystem perspective? From a biodiversity perspective, ongoing wetland protection policies may not be working because restored or created wetlands are often very different from natural wetlands. Wetland protection policies may also be inadequate to preserve and restore ecological processes such as nutrient cycling because they mostly focus on individual wetlands and ignore the fact that wetlands are integral parts of landscapes. Wetland mitigation projects, for example, often result in the exchange of one type of wetland for another and result in a loss of wetland functions at the landscape level. The most striking weakness in the current national wetlands policy is the lack of protection for ‘dry-end’ wetlands that are often the focus of debate for what is and what is not a wetland. From an ecological perspective, dry-end wetlands such as isolated seasonal wetlands and riparian wetlands associated with first order streams may be the most important landscape elements. They often support a high biodiversity and they are impacted by human activities more than other types of wetlands. The failings of current wetland protection and mitigation policies are also due, in part, to the lack of ecologically sound wetland assessment methods for guiding decision making processes. The ecologically based Hydrogeomorphic (HGM) approach to wetland assessment has the potential to be an effective tool in managing biodiversity and wetland ecosystem function in support of the national ‘No Net Loss’ policy.
Article
Peat samples from a one metre core and living Cyperaceae, collected in Tritrivakely marsh in Madagascar, were studied to determine the organic matter (OM) composition and extent of OM degradation in this core. The study was carried out combining light microscopy observations, bulk analyses, infra-red spectroscopy, hydrolyses of sugars, oxidation of lignin and pyrolyses. In the surface peat, organic matter derived from Cyperaceae undergoes extensive degradation of its basic cell wall components, morphologically revealed by destructuration of plant tissues and their transformation into reddish amorphous organic matter occurring in large amounts all along the core. Two ratios (cinnamic units/lignin and xylose+arabinose/total sugars) were determined as markers of Cyperaceae. It appeared that the vegetation of the marsh remained probably unchanged during the considered accumulation period, i.e. the last 2300 years B.P. Rhamnose, mannose and non-cellulosic glucose probably have a common origin and are mostly derived from bacteria. In contrast, galactose is likely to be a marker of algal source, especially of the diatoms that occur only in the upper part of the core (0–ca. 50 cm). Acid/aldehyde ratios of syringic and vanillic monomers (index of lignin oxidative depolymerisation) and mannose+rhamnose+non-cellulosic glucose/total sugars ratios (reflecting bacterial degradation of hemicelluloses) are positively correlated, and can thus be considered as markers of microbial degradation of the Cyperaceae tissues. The n-alkane/n-alk-1-ene doublets that dominate the pyrolysates of hydrolysed peat samples reflect the contribution of B. braunii algaenan and higher plant suberans, and of condensed lipids mostly derived from higher plants and microalgae. The upper part of the core is characterised by a greater dilution of Cyperaceae-derived compounds by organic matter from microalgae when compared with deeper samples, as recorded by peat bulk features, hydrolysable sugars, lignin oxidation products and pyrolysis products. Two accumulation periods can thus be distinguished in the core: a peaty phase between 2300 years B.P. and ca. 1500 years B.P. (low watertable and strongly limited microalgal growth); a waterlogged marsh, from ca. 1500 years B.P. to the present time, in which a higher water table was longer lasting with a substantial algal production. The environmental variation thus recorded could correspond to a regional climatic change occurring around 1500 years B.P.
Article
The sedimentary organic matter content of a series of 2-m-deep cores was investigated along a sea-land transect at five sites representing five species of mangrove and salt-marsh vegetation. The vegetation was settled at the same place for at least 1000 years and therefore sedimentary organic matter deriving from the decay of higher plants has accumulated in large amounts. The global morphological and chemical preservation of the organic matter attested by various sedimentary parameters, including the proportions of cellulose-bearing tissues, the TOC contents, the C/N ratios, the total sulphur contents and the δ13C compositions, reveals that the sedimentary organic matter is less degraded when it has been under the influence of the marine water table for a long time. This is indicated by a good correlation between the salinities of interstitial waters, the redox potentials measured in the wet sediments and the chemical composition of the organic matter. Moreover, the concentration of organic sulphur shows a positive correlation with the hydrogen index (HI), only under the marine water-table influence, suggesting the very local presence of sulphur–HC compounds.
Editor, Mires: Swamp, Bog, Fen and Moor
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Principles and Applications, American Association of Stratigraphic Palynologists Foundation Organic matter sources and early diagenetic degradation in a tropical peaty marsh Implications for environmental reconstruction during the Sub-Atlantic
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Apports de la matière organique pour la reconstitution des paléoenvironnements holocènes de la basse vallée de la Seine. Fluctuations des conditions hydrologiques locales et environnements de dépôt
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Sebag, D., 2002. Apports de la matière organique pour la reconstitution des paléoenvironnements holocènes de la basse vallée de la Seine. Fluctuations des conditions hydrologiques locales et environnements de dépôt. PhD thesis, Université de Rouen, France. Sifeddine, A., Bertrand, P., Lallier-Vergès, E., Patience, A.J., 1996. Lacustrine organic fluxes and paleoclimatic variations during the last 15 ka: Lac du Bouchet (Massif Central, France). Quaternary Science Reviews 15, 203–211.
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Sedimentary Organic Matter: Organic Facies and Palynofacies Ecological issues related to wetland preserva-tion, restoration, creation and assessment. The Science of the
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Tyson, R.V., 1995. Sedimentary Organic Matter: Organic Facies and Palynofacies. Chapman and Hall, London. Whigham, D.F., 1999. Ecological issues related to wetland preserva-tion, restoration, creation and assessment. The Science of the Total Environment 240, 31–40.
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Implications for environmental reconstruction during the Sub-Atlantic, Organic Geochemistry 21 (2000), pp. 421–438.
Relationships between organo-mineral supply and early diagenesis in the lacustrine environment: a study of surficial sediments from the Lac du
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Fluorescence et réflectance de la matière organique dispersée et évolution des sédiments
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Alpern, 1976 B. Alpern, Fluorescence et réflectance de la matière organique dispersée et évolution des sédiments, Bulletin du Centre de Recherches de Pau -SNPA 10 (1976), pp. 201–220.
Changements climatiques et effets anthropiques au cours du dernier millénaire attestés par l'étude pétrographique de la matière organique (Annecy, Le Petit Lac, France)
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Buillit et al., 1997 N. Buillit, E. Lallier-Vergès, J.R. Disnar and J.L. Loizeau, Changements climatiques et effets anthropiques au cours du dernier millénaire attestés par l'étude pétrographique de la matière organique (Annecy, Le Petit Lac, France), Bulletin de la Société Géologique de France 168 (1997), pp. 573–583.
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Analyse microtexturale des sédiments organiques du Delta de la Mahakam (Indonésie)
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