Diagenesis of organic matter in a 400 m organic rich sediment core from offshore Namibia using solid state 13C NMR and FTIR

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doi: 10.1016/j.orggeochem.2014.05.016
Author(s): Hatcher, Patrick G.; Ravin, Azdine; Behar, Françoise; Baudin, François
Author Affiliation(s): Primary:
Old Dominion University, Department of Chemistry and Biochemistry, Norfolk, VA, United States
Université Pierre et Marie Curie, France
Total Exploration and Production, France
Volume Title: Organic Geochemistry
Source: Organic Geochemistry, Vol.75, p.8-23. Publisher: Elsevier, International. ISSN: 0146-6380
Note: In English. 80 refs.; illus., incl. 4 tables, sketch map
Summary: Although rates and mechanisms of early diagenesis have been well studied, the effects of microbial metabolism on the molecular composition of the sedimentary organic matter (SOM) over long periods of time need more investigation. In this study, we characterize the early diagenesis of marine SOM from organic rich sediments of the Ocean Drilling Program site 1082 located off Namibia, in the vicinity of the Benguela coastal upwelling system. We used both Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (13C NMR) to assess the quantitative partitioning of the organic carbon into major compound classes (aliphatic, aromatic, ester, carboxylic, amide and carbons from carbohydrates). Then, we calculate the SOM composition in the main biomolecules (proteins, carbohydrates, lipids and lignin) on the basis of previous 13C NMR based estimates of the molecular composition of the organic mixtures. Results show that the SOM is still labile at 7 m below the seafloor (mbsf) and composed of about 25% proteins and 15% carbohydrates. With increasing depth, the protein content exponentially decreases to 13% at 367 mbsf, whereas the carbohydrate content decreases linearly to 11%. The lignin and lipid content consistently represent around 10% and 40% of the SOM, respectively, and show an increase with depth, due mostly to selective enrichment as the more labile components are lost by degradation. Thus, these components of the SOM are considered refractory at the depth scale considered. The calculated remineralization rates are extremely slow ranging from 5.6 mol C m-3 ky-1 at the top of the core to 0.2 mol C m-3 ky-1 according to the organic carbon flux to the seafloor. Knowing the labile carbon losses, we propose a method to calculate the initial TOC before the diagenesis took place. Abstract Copyright (2014) Elsevier, B.V.
Year of Publication: 2014
Research Program: ODP Ocean Drilling Program
Key Words: 06 Petrology, Sedimentary; Africa; Aliphatic hydrocarbons; Aromatic hydrocarbons; Atlantic Ocean; Benguela Current; Cape Basin; Cenozoic; Continental shelf; Cores; Degradation; Diagenesis; Early diagenesis; FTIR spectra; Hydrocarbons; Infrared spectra; Kerogen; Leg 175; Lignin; Marine sediments; NMR spectra; Namibia; Neogene; ODP Site 1082; Ocean Drilling Program; Ocean floors; Organic compounds; Pleistocene; Pliocene; Pyrolysis; Quaternary; Rock-Eval; Sediments; South Atlantic; Southern Africa; Spectra; Tertiary; Total organic carbon
Coordinates: S400000 S200000 E0250000 E0050000
Record ID: 2015070942
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands