Organic matter and clay interaction in a meromictic lake: Implications for source rock OM preservation (Lac Pavin, Puy-de-Dôme, France)

Abstract

International audienceInvestigation of organic matter (OM) preservation mechanisms is crucial for understanding organic accumulation in sedimentary environments. We focus here on the contribution of organo-clay interaction in such preservation. Most studies addressing this issue deal with organo-mineral complexes which have settled, omitting consideration of early aggregation within the water column. We therefore investigated the sorption of OM on montmorillonite (Na MMt) and kaolinite (Kaol) immersed in a permanently stratified water column (Lake Pavin, France). The two types of clay samples were kept immersed for different lengths of time and characterized via analytical methods suited for the organic phase [pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), GC-MS, Fourier transform infrared spectroscopy (FT-IR) and dissolved organic carbon (DOC) analysis, as well as for the mineral phase [X ray diffraction (XRD) and microprobe elementary cartography]. Results suggest that strong organo-clay interaction occurred within the water column to a varying extent depending on water physicochemical conditions and the mineral phase typology. A higher concentration of DOC was observed in the proximal environment of the clay traps, suggesting an attractive effect induced by the clay minerals. Lipid compounds sorbed during the immersion were essentially fatty acids and aromatic compounds. Their distributions were closer to a phytoplankton signature than allochtonous pedogenetic OM.The sorption was particularly efficient in the O2 transition zone, with a greater amount of OM on Na-MMt than Kaol. This was principally due to the high specific surface area and cationic exchange capacity (CEC) of the 2/1 clay mineral. Besides, XRD characterization revealed an increase in Na MMt interlayer spacing, which did not necessarily correspond to organic intercalation.The study confirms that the sorption of dissolved OM cannot alone explain the preservation of hydrocarbon-rich OM in such a lacustrine environment. Indeed, the sorbed OC was very low compared with the amount proposed by several authors as an expression of the monolayer equivalent principle

Multistage Hydrocarbon Generation of Saline Lacustrine Source Rocks in Hydrous Pyrolysis: Insights from Clay Mineral–Organic Matter Interactions

“…On the one hand, the abundant smectite (39.43 wt %) in the Y16 sample is highly chemically active due to its high SSA and negative charge . On the other hand, the primary SOM originated from reserve lipids and is therefore dominated by polar NSO compounds. , Therefore, most of the primary SOM in the Y16 sample was preferentially adsorbed by the clay minerals to form mineral-bound SOM under the interaction of organic polar functional groups with the active mineral surface. , The abundant C element in the EDS spectrum of smectite particles (Figure -1) also proves the adsorption of OM by the smectite . Mineral adsorption prevented most primary SOM from being extracted by organic solvents or released at low temperatures, so the S 1 and OSI of the original samples were relatively low and did not decrease after extraction (Figure ).…”

“…2 Therefore, thermal desorption may be more favorable for forming deep hydrocarbons, while mineral transformation-induced desorption may be more conducive to forming shallow hydrocarbons (Figure 14). Different from the degradation-recondensation preservation mechanism, 52 active minerals can directly adsorb polar compounds in the water column, 65 allowing them to be preserved from biodegradation. 9 Mineral-bound SOM can be further desorbed and defunctionalized during diagenesis to form hydrocarbons with similar components to petroleum (Figure 14).…”

Over-sulfated soils and sediments treatment: A brief discussion on performance disparities of biological and non-biological methods throughout the literature

“…Low pH is acknowledged as a promoting factor for sorptive processes. It is indeed well recognized that acidic conditions enhance the uptake of both inorganic and organic ions (Mahamat Ahmat et al, 2016, 2017; Nodvin et al, 1986; Thiebault and Boussafir, 2019). By controlling the protonation and deprotonation state of mineral surfaces, background acidity affects the distribution of electrical charges (Park et al, 2002; Tournassat et al, 2016), thus constraining the intensity of the sorptive mechanism.…”

Modified Red Muds and Slag Based Hydraulic Binders for Zn Removal: A Matrix-Spiking Approach Applied on Clayey Sediments

“…Sedimentary lipids were extracted using accelerated solvent extraction (ASE 200, Dionex ® ) with CH 2 Cl 2 :MeOH (9:1 v/v) at 100 • C and 1000 psi. The extract was separated into neutral, acidic and polar fractions using solid phase extraction on aminopropyl bonded silica as described in [51,52]. The acid fraction was methylated with anhydrous MeOH/MeCOCl by heating at 60 • C for 1 h. An internal standard (5α-cholestane, 100 µL) was added to each fraction for quantification.…”

“…Langmuir model supposes that the adsorbates are retained on individualized sites across the accessible surface, and each site hosts a unique ion. It calculated via the equation [52].…”