Stable Isotopic, Micro-FTIR, and Geochemical Characteristics of the Permian Madzaringwe Shale of Tuli Basin, South Africa: Implications for Organic-Rich Shale Provenance

Abstract

The paleo-environmental setting of an organic-rich shale remains an essential controlling factor for shale reservoir distribution. The scarcity of generalised data on paleo-environment settings has been spurred using a simple investigative approach to decipher the provenance of organic-rich shale in various regions. This study investigates the organic-rich Madzaringwe shale of the Tuli Basin to reconstruct the provenance of the organic material for shale gas generation potential. Representative shale core samples were analysed for the stable isotopic fractions, functional groups, and major and trace compositions. The carbon isotopic composition, δ13C value, ranging from −21.01 to −24.0‰, averaging at −22.4‰. Inference from the stable isotopic compositions and functional group analysis indicate Type-III kerogen prone to gas generation in the studied Madzaringwe shale. The micro-Fourier transformed infrared (micro-FTIR) analysis reveals infrared absorption peaks between 2800 and 3300 cm−1 wavelengths corresponding to gaseous hydrocarbon. The x-ray fluorescence (XRF) result reveals major elements comprising Al2O3 (29.25–29.11%), CaO (0.29–0.28%), Fe2O3 (1.16–1.09%), K2O (0.97–0.98%), MgO (0.13–0.12%), Na2O (0.12–0.09%), P2O5 (0.22–0.21%), SiO2 (52.50–52.30%), and TiO2 (1.20–1.18%). The major element ratio of Al2O3/TiO2 values ≥ 25 indicates felsic and intermediate provenance from a terrigenous paleo-environment. In addition, laser ablation inductively coupled plasma mass spectrometry (LAICP-MS) reveals the trace elements in which elemental proxy of V/(V + Ni) with a value greater than 0.5 represent reducing environments. Furthermore, the geochemical proxies and isotopic compositions have revealed an anoxic paleo-environment for the non-marine-derived organic matter in the studied carbonaceous shale.