Correction for the siderite effect on Rock-Eval parameters: Application to the sediments of Lake Barombi (southwest Cameroon)

• Published in: Organic geochemistry 2018-09, Vol.123, p.126-135
• Main Authors: Sebag, David, Garcin, Yannick, Adatte, Thierry, Deschamps, Pierre, Ménot, Guillemette, Verrecchia, Eric P.
• Format: Article
• Language: English
• Subjects: Continental interfaces, environment; Earth Sciences; Geochemistry; Organic geochemistry; Rock-Eval pyrolysis; Sciences of the Universe; Siderite; Tropical lake; Van Krevelen diagram; Western Central Africa
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/j.orggeochem.2018.05.010

•Standard Rock-Eval parameters provide valuable information about organic and inorganic carbon.•Presence of siderite in lake sediments can disturb this information.•A thermogram analysis is proposed to correct for the effect of siderite.•Siderite-effect-free parameters accurately reflect changes in sedimentary organic matter. Originally developed for use in the petroleum industry, Rock-Eval pyrolysis is a technique commonly applied to lake sediments to infer paleoenvironmental reconstructions. The standard Rock-Eval parameters provide information on the amount of total organic and inorganic carbon (TOC and MinC, respectively), and are usually interpreted as proxies for the source (aquatic or terrestrial) of the primary production of organic matter (Hydrogen Index vs Oxygen Index). Although this method usually provides valuable evidence, the common presence of siderite in tropical lake sediments can alter the primary signal of the sedimentary organic matter (SOM). Indeed, the CO2 and CO released by the pyrolysis of siderite are integral to the calculation of the SOM-related standard Rock-Eval parameters. In this study, we analyze sediments from a core collected in the Lake Barombi (southwest Cameroon) and describe the impact of siderite on standard Rock-Eval parameters. We propose a workflow that allows standard Rock-Eval parameters to be corrected, based on the analysis of thermograms. The proposed corrections provide siderite-effect-free parameters, accurately reflecting the changes in sedimentary organic matter composition.