Geochemical and mineralogical characteristics of shales from the early to middle Permian Dohol Formation in Peninsular Malaysia: Implications for organic matter enrichment, provenance, tectonic setting, palaeoweathering and paleoclimate

The early to middle Permian Dohol Formation is characterized by a significant presence of shale deposits. While these shales exhibit a low potential to generate hydrocarbons, there is a need to ascertain the possible reasons for the low hydrocarbon generation potential. Also, there are several unidentified properties and attributes associated with these shales in terms of their inorganic geochemical characteristics and their mineralogy. This study is focused on using XRF, ICPMS, and SEM with EDX to determine the mineralogical and geochemical characteristics of these shales and use these data to discuss their provenance history and tectonic setting and interpret the paleoclimatic and paleoweathering conditions. The inorganic geochemical analysis shows that the shales from the Dohol Formation are from a felsic igneous source. The shales were also identified to be from a passive margin based on the bivariate plot of SiO2 vs log (K2O/Na2O) and several multidimensional diagram plots. The CIA and CIW data, as well as the A-CN-K plot, all point to a significant degree of chemical weathering, ranging from mild to intense. The Sr/Cu ratio and C-value, combined with various other geochemical proxies, indicate that the shales were formed in warm-humid climatic conditions. The SEM analysis shows that the samples are mainly composed of kaolinite and illite, and this result was supported by the EDX elemental composition. The high terrigenous influx of sediments, the oxic to sub-oxic conditions in which the sediments were deposited, and finally low marine productivity were found to be the reasons for the low TOC in the shales from the Dohol Formation.

Application of stable isotope of water and a Bayesian isotope mixing model (SIMMR) in groundwater studies: a case study of the Granvillebrook and Kingtom dumpsites

The increase in groundwater salinity of the two major dumpsites in Sierra Leone has been a major concern for stakeholders. Therefore, this study employed geochemical and stable water isotope analyses to investigate the factors controlling groundwater salinity. The proportional sources of the groundwaters were also evaluated using the Bayesian isotope mixing model. The geochemical analysis showed that the groundwater chemistry in the Granvillebrook dumpsite is controlled by water-rock interaction and evaporation while that of the Kingtom is dominated by water-rock interaction and precipitation. The biplot of deuterium (δ²H) versus oxygen (δ¹⁸O) composition relative to the global meteoric water line confirms that the groundwaters of the study areas are of meteoric origin. The linear plot of electrical conductivity versus δ¹⁸O depicts that mineralization is the major factor impacting the groundwater salinity in the study areas. The stable isotope mixing model in R (SIMMR) suggests that 96.5% of the groundwaters in the study areas are recharged by precipitation while only 3.5% originated from surface water. The SIMMR model also depicts that groundwaters in the Granvillebrook dumpsite have been bridged by leachate (33.0%) and domestic wastewater (15.2%) while for the Kingtom dumpsite, 13% and 21.5% are contaminated by leachate and domestic wastewaters. Contrary to other previous studies, this research confirms the feasibility of using the Bayesian isotope mixing model to quantify the factors influencing groundwater salinity.