The Niger River drains a large part of the West African Craton, where rocks ranging in age from Paleoarchean to recent offer an unexcelled opportunity to map the diverse time structures of sediment sources and provide essential information for provenance diagnoses. In this study, U-Pb zircon dating is complemented with bulk-sand geochemical (Zr, Hf, REE) and Nd-Hf isotope data to pin-point parent rocks of zircon grains and draw inferences on sediment generation across sub-Saharan western Africa. In Upper Niger sand, zircon ages pass from exclusively Archean in Guinea headwaters to dominantly Paleoproterozoic in the Inner Delta in Mali, testifying to the progressive dilution by tributary sediment derived from the Birimian domain. Zircon ages abruptly change to dominantly Neoproterozoic downstream of the Inner Delta, becoming indistinguishable from those in Saharan eolian dunes across the Sahel. Most of the sediment generated in the headwaters is thus dumped in the marshlands and bedload is reconstituted downstream by recycling eolian sand. Zircon grains in the Lower Niger yielded virtually the same U-Pb ages as in Benue sediment, indicating an overwhelming supply from the Benue tributary. In the Niger Delta, however, Archean zircons reappear, and both ε_Nd and ε_Hf values become notably more negative, indicating extensive reworking of sand deposited along the coastal plain at earlier times of wetter climate, when artificial barriers to the sediment flux did not exist in the upper to middle Niger River catchment.

中文翻译：

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尼日尔河的锆石故事：西非克拉通的时间结构图和物源信号在​​不相连的沉积物路由系统中的不连续传播

尼日尔河流经西非克拉通的大部分地区，那里的岩石年龄从古太古代到近代，为绘制沉积物来源的不同时间结构提供了绝佳的机会，并为来源诊断提供了重要信息。在这项研究中，U-Pb 锆石定年法与散装砂地球化学（Zr、Hf、REE）和 Nd-Hf 同位素数据相辅相成，以查明锆石颗粒的母岩，并对撒哈拉以南非洲西部的沉积物生成进行推断。在尼日尔上游的沙子中，锆石年龄从几内亚源头的太古宙过渡到马里内三角洲的古元古代，这证明了来自比里米亚域的支流沉积物的逐渐稀释。内三角洲下游的锆石年龄突然转变为主要是新元古代，与萨赫勒地区撒哈拉风成沙丘的锆石年龄变得难以区分。因此，源头产生的大部分沉积物都被倾倒在沼泽地中，并通过回收风积沙在下游重建河床负荷。尼日尔下游的锆石颗粒产生的 U-Pb 年龄几乎与贝努埃沉积物相同，表明贝努埃支流的供应量巨大。然而，在尼日尔三角洲，太古代锆石再次出现，并且 ε _Nd和 ε _Hf值都显着变得更负，这表明在气候湿润的早期，当沉积物通量的人为障碍没有发生时，沿着沿海平原沉积的沙子发生了广泛的改造。分布于尼日尔河中上游流域。