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首页> 外文期刊>Journal of African Earth Sciences >Campano-Maastrichtian paleoenvironment, paleotectonics and sediment provenance of western Anambra Basin, Nigeria: Multi-proxy evidences from the Mamu Formation
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Campano-Maastrichtian paleoenvironment, paleotectonics and sediment provenance of western Anambra Basin, Nigeria: Multi-proxy evidences from the Mamu Formation

机译：尼日利亚阿南布拉盆地西部的坎帕诺-马斯特里赫特古环境，古构造和沉积物来源：马姆组的多代理证据

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This article presents the results of a high-resolution evaluation of the sedimentological, mineralogical, palynofacies, and geochemical aspects of the Mamu Formation aimed at deciphering the sediment provenance, as well as the prevailing paleoenvironmental, paleoclimatic and paleotectonic conditions that occurred during the late Campanian-middle Maastrichtian age in the less studied western section of the Anambra Basin, Nigeria. Four measured sections exposed in Uzebba (composite), Auchi, Okpekpe, and Imiegba were investigated using sedimentological (outcrop studies and laser diffraction particle size analysis), mineralogical (XRD), geochemical (ICP-MS and XRF) and palynofacies techniques. Seven lithofacies were identified and grouped into central basin, marsh, bay, barrier, beach, and washover fan facies association as well as meandering fluvial-tidal channel fades association interpreted as indicative of a tidally influenced wave dominated estuarine paleoenvironment. In addition, mineralogical and palynofacies characterization revealed the heterogeneous nature of the dark mudstone lithofacies, varying from a more proximal low salinity phytoclast and quartz dominated marsh and bay mudstones to a more distal higher salinity palynomorph and clay dominated central basin accumulating deep-water mudstones. Consistent with recent Campano-Maastrichtian paleogeographic and paleoclimatic models we observed a dominance of kaolinite, a high chemical index of alteration above 90%, and a predominantly low index of compositional variability values ( 1%), which signifies mineralogical maturity of the sediments due to sediment recycling and intensive chemical weathering under humid tropical paleoclimate. Furthermore, trace and major element discriminant plots revealed a felsic-intermediate provenance for the sediments under passive margin paleotectonic regime, which is in agreement with the regional distribution, geology, and geochemistry of the pre-Santonian rocks and the Precambrian basement rocks in the area.
机译：本文介绍了对Mamu组的沉积学，矿物学，古岩相和地球化学方面进行高分辨率评估的结果，旨在破译沉积物来源以及在Campanian晚期发生的普遍的古环境，古气候和古构造条件-尼日利亚阿南布拉盆地西部研究较少的马斯特里赫特中期。使用沉积学（露头研究和激光衍射粒度分析），矿物学（XRD），地球化学（ICP-MS和XRF）和古相技术研究了在Uzebba（复合材料），Auchi，Okpekpe和Imiegba中暴露的四个测量部分。确定了七个岩相，并将其分为中央盆地，沼泽，海湾，屏障，海滩和冲刷扇相相结合，以及蜿蜒的潮汐-河道消退相联系，这被解释为潮汐作用主导的河口古环境。此外，矿物学和古岩相特征揭示了深色泥岩岩相的非均质性质，从较近的低盐度植物碎屑岩和石英为主的沼泽和海湾泥岩，到较远的较高盐度的古粉质岩和以粘土为主的中央盆地堆积的深水泥岩。与最近的Campano-Maastrichtian古地理和古气候模型一致，我们观察到高岭石占主导地位，化学变化指数高于90％且组成变异性值指数（<1％）主要较低，这表明该沉积物的矿物学成熟度在潮湿的热带古气候下沉积物的循环利用和强烈的化学风化作用。此外，痕量和主要元素判别图揭示了被动边缘古构造条件下沉积物的长英质-中源，这与该地区之前的桑顿时期的岩石和前寒武纪的基底岩石的区域分布，地质和地球化学相符。 。

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