Palaeontological deposits on Rusinga Island, Lake Victoria, Kenya, provide a rich record of floral and faunal evolution in the early Neogene of East Africa. Yet, despite a wealth of available fossil material, previous palaeoenvironmental reconstructions from Rusinga have resulted in widely divergent results, ranging from closed forest to open woodland environments. Presented here is a detailed study of the sedimentology and fauna of the early Miocene Hiwegi Formation at Waregi Hill on Rusinga Island, Kenya. New sedimentological analyses demonstrate that the Hiwegi Formation records an environmental transition from the bottom to the top of the formation. Lower in the Hiwegi Formation, satin‐spar calcite after gypsum in siltstone deposits are interpreted as evidence for open hypersaline lakes. Moving up‐section, carbonate deposits – interpreted previously as evidence of aridity – are actually diagenetic calcite cements, which preserve root systems of trees, suggesting a more closed environment; further up‐section, the uppermost palaeosol layer contains abundant root traces and tree‐stump casts, previously reported as evidence of a closed‐canopy forest. These newly interpreted environmental differences are reflected by differences in faunal composition and abundance data from Hiwegi Formation fossil sites R1 and R3. Taken together, this work suggests that divergent palaeoenvironmental reconstructions in previous studies may have been informed by time‐averaging across multiple environments. Further, results demonstrate that during the early Miocene local or regional habitat heterogeneity already existed. Rusinga’s Hiwegi Formation varied both spatially and temporally, which challenges the interpretation that a broad forested environment stretched across the African continent during the early Neogene, transitioning later to predominately open landscapes that characterize the region today. This result has important implications for interpretations of the selective pressures faced by early Miocene fauna, including Rusinga Island’s well‐preserved fossil primates.

中文翻译：

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肯尼亚维多利亚湖Rusinga岛Hiwegi组（中新世早期）Waregi Hill的沉积学和古环境研究

肯尼亚维多利亚湖Rusinga岛上的古生物学沉积物提供了东非新近纪早期花卉和动物区系演化的丰富记录。然而，尽管有大量可用的化石材料，但以前从鲁西加（Rusinga）进行的古环境重建带来了大不相同的结果，从封闭的森林到开阔的林地环境。这里介绍的是肯尼亚Rusinga岛Waregi Hill上的中新世Hiwegi组早期沉积学和动物区系的详细研究。新的沉积学分析表明，Hiwegi地层记录了从地层底部到顶部的环境转变。在Hiwegi组的下部，粉砂岩沉积物中的石膏之后的缎晶晶石方解石被解释为开放高盐湖的证据。向上移动 碳酸盐矿床（以前被解释为干旱的证据）实际上是成岩方解石水泥，它保留了树木的根系，表明环境更加封闭。再往上看，最上层的古土壤层含有丰富的根迹和树桩，以前被报道为封闭林冠的证据。这些新解释的环境差异反映在Hiwegi组化石遗址R1和R3的动物组成和丰度数据上。两者合计，这项工作表明以前的研究中不同的古环境重建可能是通过跨多个环境的时间平均来获得的。此外，结果表明，在中新世早期，局部或区域生境已经存在异质性。鲁辛加（Rusinga）的希维吉（Hiwegi）编队在空间和时间上都在变化，这对以下解释提出了挑战，即在新近纪早期，广阔的森林环境遍布整个非洲大陆，后来又过渡到如今是该地区主要特征的开放景观。这一结果对于解释早期中新世动物群（包括鲁辛加岛保存完好的化石灵长类动物）面临的选择压力具有重要意义。