Technical note: assessing pretreatment approaches for serial pyrolysis-oxidation analysis of sedimentary organic carbon

Abstract

Ramped-temperature pyrolysis/oxidation (RPO) analysis has emerged as a powerful analytical technique for characterizing sedimentary organic carbon (OC) provenance and reactivity, bridging the knowledge gap between bulk carbon isotopic measurement and molecular-level biomarker analyses. While acid pretreatment is routinely employed to remove carbonates prior to RPO analysis, its methodological impacts remain poorly constrained compared to other geochemical measurements (e.g., δ13C). Given the widespread utilization of RPO analysis in recent studies, a comparative examination of pretreatment conditions is timely to ensure unbiased acquisition of thermochemical results. This study systematically evaluates how decarbonation protocols influence RPO results through comparative analyses of different pretreatment approaches. We demonstrate that both acidification method (rinsing vs. fumigation) and HCl concentration significantly affect RPO thermograms, with observed differences attributed to the alteration of organic-inorganic associations and selective leaching of acid-soluble OC. Generally, results from diluted acid rinsing are more similar to the raw material. Based on comprehensive testing, we recommend diluted (i.e., 1 N) HCl rinsing with moderate reaction times (∼ 12 h) as the optimal pretreatment conditions for most samples, while acknowledging that specific sample characteristics (e.g., organic lean, protein rich) may necessitate adjustments to the protocol. These finding highlight the importance of pretreatment conditions in thermochemical decomposition studies.