In 2014, Pillot et al. [Identification and quantification of carbonate species using Rock-Eval pyrolysis, Oil Gas Sci. Technol. – Rev. IFP 69, 341–349. https://doi.org/10.2516/ogst/2012036] proposed to use the Rock-Eval^® method as a reliable tool to identify and quantify carbonates in solid samples from the CO₂ flux emitted by their progressive thermal decomposition during programmed heating under oxidant atmosphere. Nevertheless, several phenomena associated with the thermal decomposition of carbonates were not explained by these authors. This paper attempts to explain these phenomena by adding 5 new carbonate species to the 9 studied by Pillot et al. https://doi.org/10.2516/ogst/2012036 and by developing a kinetic approach to the thermal decomposition of carbonates. It appears that the kinetics of thermal decomposition of most carbonates is not of order 1 but varies according to carbonate species. Consequently, the thermal decomposition temperature varies with both the sample weight and the temperature rate applied. The thermal stability of simple carbonates is explained by the electronegativity of the cations associated with the carbonate anion. Our study provides further insights into the use of Rock-Eval^® for the identification and quantification of different carbonate species.

Siderite (FeCO₃) is an iron carbonate present in Archean and Neoproterozoic Banded Iron Formations (BIFs) as well as in much more recent sedimentary basins. Due to its high iron content, it could be part of H₂ systems, and we have quantified its potential as a H₂-generating rock and its kinetics from samples from the Llanos Basin in Colombia and from the Solimões Basin in Brazil. The H₂ potential of natural siderite-rich Cenozoic formations was measured with a Hydrogen-Eval pyrolyzer, where the H₂ yield depends linearly on the siderite content of the rock. It reaches 3.5 mol/kg for a sample containing 50% of siderite. The siderite is known to be unstable and to decompose at relatively low temperatures, between 100 and 200 °C. These results suggest that sedimentary siderite could be an additional potential H₂-generating rock, through oxido-reduction, with an active H₂ generation window between 3 and 6 km. In sedimentary basin at these depths, reservoirs and traps are likely to be present, and the porosity could be ideal for accumulation. Strong external water supply through hydrodynamics will promote H₂ generation, but the dehydration of rocks such as clays will also enable it through local water supply.

This study assesses the hydrocarbon potential of the Permian Karoo sedimentary rocks within the Siamwiinga area of Zambia's Mid-Zambezi Basin. While highly prospective Karoo source rocks, such as the prolific Ecca Group in South Africa, are recognised regional analogues, the specific characteristics of the Madumabisa and Gwembe Formations in this sector remain poorly constrained. This assessment aims to rectify this critical knowledge gap, providing essential data for regional exploration. To address this gap, an integrated analysis of Rock-Eval pyrolysis (34 samples) and palynofacies data (36 samples) was undertaken to determine organic richness, kerogen type and thermal maturity. Geochemical analyses reveal wide-ranging TOC values (0.02–37.47 wt-%), indicating poor to excellent organic matter content. Cross-plots of HI (8–404 mg HC/g TOC) versus Tmax and OI suggest mixed kerogen types (II, II/III, III and IV). Over 50% of the samples, including coal, carbonaceous mudstone and coaly shale, display Tmax values of 430 °C–470 °C, representing maturity stages from the main oil window (435 °C–460 °C) to the late oil–early gas window (∼470 °C). These results imply active hydrocarbon generation across different parts of the basin, with potential for both liquid and gaseous hydrocarbons. Palynofacies analysis, showing a predominance of sporomorphs, phytoclasts and inertinite, further confirms geochemical interpretations. The findings confirm a viable hydrocarbon system within the Madumabisa and Gwembe Formations, providing the first detailed geochemical and palynological insights into this specific region and thereby reducing future exploration risk.