喀麦隆巴门达大学George Lemewihbwen Ngiamte团队研究了喀麦隆库姆盆地白垩系泥岩古沉积环境、物源和古气候的矿物学、地球化学和稳定同位素重建。相关论文于2025年7月1日发表在《地球化学学报》杂志上。

白垩纪库姆盆地是喀麦隆北部一个与裂谷有关的半地堑，是上贝努埃海槽约拉臂的一部分。该研究首次综合了盆地深灰色细粒泥岩的矿物学、大块岩石地球化学和稳定的碳氢氧同位素数据，为盆地沉积强度、古环境和地球动力学背景提供了新的认识。泥岩主要由层状硅酸盐（~ 8.6%）、长石（~ 30.5%）、碳酸盐（~ 13.7%）和少量氧化铁（~ 2.7%）组成，粘土矿物主要为蛭石、伊利石和高岭石。

安钙石、铁云母和白云石的存在表明其变质程度较低和/或热液蚀变。Fe₂O₃/K₂O（1.52 ~ 6.40）和SiO₂/Al₂O₃（2.97 ~ 4.68）比值将泥岩划分为成分不成熟的页岩（ICV ~ 1.64），具有中低化学风化作用（CIA ~ 56.35）；Pia ~ 59.74；R³⁺/R³⁺ + R²⁺ + M⁺ ~ 0.51)。微量元素比值（Th/Sc ~ 1.70, Zr/Sc ~ 1.33, La/Sc ~ 6.30, La/Th ~ 4.14）表明其火成岩物源为陆相。

古环境指标显示沉积环境为动态盆地环境，其特征是氧化还原（C_org/P: 0.21-178.34）和盐度（Sr/Ba: 0.34-3.25；n值：48-35.92)，从缺氧到无氧，从微咸到盐水。主要元素数据（SiO₂ vs. Al₂O₃ + K₂O + Na₂O）表明古气候条件为半干旱，而Sr/Cu（1.88 ~ 37.47）和c值（0.12 ~ 0.93）表明古气候条件为湿润和干旱交替。值得注意的是，库姆盆地首次报道的稳定同位素数据显示，有机碳(δ¹³C 25.2‰到(δ¹⁸O + 3.6‰~ + 24.9‰，δ²H 104‰到50‰)。综合矿物学、地球化学和同位素数据表明，沉积在一个构造活跃的大陆弧环境中，并有海洋岛弧和被动边缘的贡献。

附：英文原文

Title: Mineralogy, geochemistry, and stable isotopes in the reconstruction of the paleodepositional environment, provenance, and paleoclimate of Cretaceous mudstones, Koum Basin, Cameroon

Author: Njamnsi, Nowel Yinkfu, Ngiamte, George Lemewihbwen, Suh, Cheo Emmanuel, Njoh, Olivier Anoh, Layton-Matthews, Daniel, Pufahl, Peir K., Dobosz, Agatha

Issue&Volume: 2025-07-01

Abstract: The Cretaceous Koum Basin is a rift-related half-graben in northern Cameroon, which constitutes a portion of the Yola Arm of the Upper Benue Trough. This study presents the first comprehensive dataset combining mineralogical, bulk-rock geochemical, and stable C–H–O isotopic data for dark-gray, fine-grained mudstones from the basin, providing new insights into its sediment source, paleoenvironment, and geodynamic setting. The mudstones primarily consist of phyllosilicates (~ 8.6%), feldspars (~ 30.5%), carbonates (~ 13.7%), and minor iron oxides (~ 2.7%), with vermiculite, illite, and kaolinite as the main clay minerals. The presence of analcime, ankerite, and dolomite suggests low-grade metamorphism and/or hydrothermal alteration. Fe2O3/K2O (1.52–6.40) and SiO2/Al2O3 (2.97–4.68) ratios classify the mudstones as compositionally immature shales (ICV ~ 1.64) with low-moderate chemical weathering (CIA ~ 56.35; PIA ~ 59.74; R3+/R3+ + R2+ + M+  ~ 0.51). Trace element ratios (Th/Sc ~ 1.70, Zr/Sc ~ 1.33, La/Sc ~ 6.30, La/Th ~ 4.14) indicate an intermediate igneous provenance from a continental crustal source. Paleoenvironmental proxies suggest deposition in a dynamic basin environment marked by fluctuating redox (Corg/P: 0.21–178.34) and salinity (Sr/Ba: 0.34–3.25; N-values: 48–35.92) conditions, ranging from oxic to anoxic and brackish to saline. Major element data (SiO2 vs. Al2O3 + K2O + Na2O) indicate a semi-arid regime, while Paleoclimatic indicators such as Sr/Cu (1.88–37.47) and C-values (0.12–0.93) suggests alternating humid and arid conditions. Notably, stable isotope data, reported here for the first time in the Koum Basin, reveal a predominantly terrestrial, fluvial-deltaic C3 plant source for organic carbon (δ13C 25.2‰ to 35.2‰) and complex fluid-rock interactions involving meteoric and magmatic-metamorphic fluids under a warm, equatorial climate (δ18O + 3.6‰ to + 24.9‰, δ2H 104‰ to 50‰). The combined mineralogical, geochemical, and isotopic data point to deposition in a tectonically active continental arc setting, with contributions from ocean island arc and passive margin sources.

DOI: 10.1007/s11631-025-00800-y

Source: https://link.springer.com/article/10.1007/s11631-025-00800-y