Abstract Geochemical signatures of sedimentary rocks provide reliable proxies that allow a better understanding of sedimentary processes. The geochemical compositions of Awgu Shale (southern Benue Trough) and Enugu Shale (Anambra Basin), south-eastern Nigeria, were investigated to appraise the degree of source area weathering and reconstruct the provenance and paleo-depositional environment. High values of several weathering indices such as Chemical index of alteration (CIA; 91.26 ± 3.26), Chemical Index of Weathering (CIW; 98.78 ± 1.42), Plagioclase Index of Alteration (PIA; 98.64 ± 1.62) and the Al2O3-(CaO + Na2O)–K2O ternary relationship indicate intense weathering in the source area. The remarkable enrichment in light rare-earth elements (LREE), the negative Eu anomalies (0.77 ± 0.06) and elemental ratios (La/Sc, La/Co, Th/Co, Th/Cr, Cr/Th, and Th/Sc) diagnostic of provenance suggest derivation from predominantly felsic sources. The results also provide clues of the tectonic settings and suggest deposition on a passive margin. The signals of redox proxies (Ni/Co, V/Cr, Cu/Zn, U/Th, Ce/Ce*) reflect predominantly oxic conditions while the Sr/Ba ratios (0.25–2.04) suggests alternated marine and continental paleo-depositional settings. The inorganic geochemical proxies of weathering, provenance, salinity, and redox conditions reflect an insignificant disparity between the pre-Santonian Awgu Shale and the post-Santonian Enugu Shale.

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揭开尼日利亚东南部部分泥岩物源特征和古沉积环境的神秘面纱：地球化学的限制

摘要 沉积岩的地球化学特征提供了可靠的代理，可以更好地了解沉积过程。研究了尼日利亚东南部Awgu页岩（贝努埃海槽南部）和Enugu页岩（阿南布拉盆地）的地球化学成分，评价源区风化程度，重建物源和古沉积环境。几个风化指数的高值，如化学蚀变指数 (CIA; 91.26 ± 3.26)、化学风化指数 (CIW; 98.78 ± 1.42)、蚀变斜长石指数 (PIA; 98.64 ± 1.62) 和 Al2O3-(CaO + Na2O)-K2O 三元关系表明源区风化强烈。轻稀土元素（LREE）显着富集，Eu负异常（0.77±0.06）和元素比（La/Sc，La/Co，Th/Co，Th/Cr，Cr/Th，和 Th/Sc) 的出处诊断表明主要来源于长英质来源。结果还提供了构造环境的线索，并建议在被动边缘沉积。氧化还原代理（Ni/Co、V/Cr、Cu/Zn、U/Th、Ce/Ce*）的信号主要反映了有氧条件，而 Sr/Ba 比率（0.25-2.04）表明交替的海洋和大陆古沉积设置。风化、来源、盐度和氧化还原条件的无机地球化学指标反映了桑顿阶前的奥古页岩和桑顿阶后的埃努古页岩之间的微不足道的差异。Ce/Ce*) 主要反映有氧条件，而 Sr/Ba 比 (0.25-2.04) 表明交替的海洋和大陆古沉积环境。风化、来源、盐度和氧化还原条件的无机地球化学指标反映了桑顿阶前的奥古页岩和桑顿阶后的埃努古页岩之间的微不足道的差异。Ce/Ce*) 主要反映有氧条件，而 Sr/Ba 比 (0.25-2.04) 表明交替的海洋和大陆古沉积环境。风化、来源、盐度和氧化还原条件的无机地球化学指标反映了桑顿阶前的奥古页岩和桑顿阶后的埃努古页岩之间的微不足道的差异。