Assessment of organic-rich hydrocarbon source rock potential of Permian Karoo strata,Siamwiinga area,Mid-Zambezi Basin,Zambia: An integrated Rock-Eval and palynofacies study

Abstract

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.