Mineralogical and geochemical changes in subsurface shales straddling the Ordovician–Silurian boundary in the eastern Kufra Basin, Libya

This paper reports on the elemental geochemistry of 47 shale samples from uppermost Hirnantian–lowermost Rhuddanian Tanezzuft Formation, collected drill core (depth interval 20.8–73.2 m) borehole JA-2 at eastern Kufra Basin, SE Libya. Eighteen these were also analysed by X-ray diffraction. study was carried out (i) to search for shales with high total organic carbon (TOC >3 wt%) and associated uranium (U > 30 ppm) concentrations, commonly referred as ‘hot’ shales, (ii) test whether TOC U correlate, (iii) effects surface weathering behaviour mobility major oxides, trace elements rare earth (REE), (iv) examine relationship composition obtained in this Rock-Eval pyrolysis kerogen data previous studies same samples. The studied can be divided into three intervals: upper weathered section (20.8–46.5 m, influenced Quaternary weathering), unweathered (46.5–68.5 m), lower (68.5–73.9 latest Ordovician weathering). Overall, have low values (<1 concentrations (<12 ppm). do not show any correlation likely due their values. Hence, has yet been proven part Basin. Trace such Mn Sc significant changes section. In contrast, majority REE seem unaffected or least largely processes. exception is transition core. Here, most either abrupt gradual shifts towards higher element concentrations. observed whole-rock geochemical (e.g., K2O, Rb, Sr, Th/K) mineralogical kaolinite/illite, K-feldspar/quartz) suggest a switch one source area another or, more likely, climatic influence. deepest may humid warm climate that led intensive chemical dissolution K-feldspar. During Hirnantian–earliest temporary emersion event occurred post-glacial rebound, which older strata.