Abstract As part of the Hominin Sites and Paleolakes Drilling Project (HSPDP), phytoliths, pollen, and microcharcoal were examined from the 228 m (3.29 to 2.56 Ma) Baringo-Tugen Hills-Barsemoi drill core (BTB13). A total of 652 samples were collected at ~10 to 32 cm intervals, corresponding to sub-millennial to millennial scale temporal resolution. Microcharcoal was well-preserved throughout the core and often peaked in abundance ~5 kyr before and after insolation peaks. Phytolith preservation varied between excellent to total dissolution in alternating intervals throughout the core. Pollen was rarely preserved. These combined datasets indicate that prior to ~3.1 Ma, woody cover fluctuated between open savanna ( 80% cover) at typically precessional (19–23 kyr) periodicities. During the mid-Piacenzian Warm Period (MPWP; 3.26–3.01 Ma), intervals with exceptionally high microcharcoal abundance suggest that regional turnover from wooded to open habitats was driven in part by fire. After ~3.1 Ma, low-elevation woody cover likely never exceeded 40%, with oscillations between mesic tall-grass vs. xeric short-grass savanna at precessional periodicities. Mesic C4 tall-grass (Panicoideae) peaked in abundance during insolation maxima, whereas xeric C4 short-grass (Chloridoideae) peaked during insolation minima. The onset of Northern Hemisphere glaciation (NHG) at ~2.75 Ma coincided with the appearance of deep lake phases and increases in grass density and fire frequency. Spectral analysis and intervals with well-preserved phytoliths indicate that precession and interhemispheric insolation gradients influenced vegetation via their effects on equatorial precipitation and fire. This study fills a crucial gap in Pliocene vegetation reconstructions from the East African Rift Valley and its associated hominin localities. It also provides orbitally resolved regional vegetation data useful in paleodata–model comparisons for the onset of the MPWP (which is often used as an analog for future warming) and NHG.

中文翻译：

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来自肯尼亚巴林戈盆地的植硅体、花粉和微炭揭示了上新世-更新世过渡期间的稀树草原动态

摘要 作为 Hominin Sites and Paleolakes Drilling Project (HSPDP) 的一部分，从 228 m (3.29 to 2.56 Ma) Baringo-Tugen Hills-Barsemoi 钻芯 (BTB13) 中检测了植硅体、花粉和微炭。总共以约 10 到 32 厘米的间隔收集了 652 个样本，对应于亚千禧年到千禧年的时间分辨率。微炭在整个核心中保存完好，并且通常在日晒峰值前后达到约 5 kyr 的丰度峰值。在整个岩心的交替间隔中，植硅体保存在极好到完全溶解之间变化。花粉很少被保存。这些组合数据集表明，在~3.1 Ma 之前，木质覆盖在开阔的稀树草原（80% 覆盖）之间以典型的岁差（19-23 kyr）周期波动。在皮亚琴察中期暖期（MPWP；3.26-3.01 Ma），具有异常高微炭丰度的间隔表明，从树木繁茂的栖息地到开阔的栖息地的区域转换部分是由火驱动的。在~3.1 Ma 之后，低海拔木质覆盖可能永远不会超过 40%，在岁差周期中，中等高草与干旱短草稀树草原之间的振荡。Mesic C4 高草（Panicoideae）在日照最大值期间达到峰值，而干旱 C4 短草（Chloridoideae）在日照最小值期间达到峰值。北半球冰期 (NHG) 在 ~2.75 Ma 开始与深湖相的出现以及草密度和火灾频率的增加相吻合。光谱分析和保存完好的植硅体间隔表明，进动和半球间日照梯度通过对赤道降水和火灾的影响来影响植被。这项研究填补了东非大裂谷及其相关人类地区上新世植被重建的关键空白。它还提供轨道分辨的区域植被数据，可用于 MPWP（通常用作未来变暖的模拟）和 NHG 开始的古数据模型比较。