The accurate paleoelevation reconstruction of the Qilian Mountains is critical to advancing our understanding the integrity of the Tibetan Plateau (TP) uplift model, its deep structural mechanisms, and corresponding connections with climatic, environmental, and biodiversity changes. Recently, the first quantitative reconstruction of the paleomidrange (i.e., average elevation of the basin and mountains) of the northern Tibetan Plateau (NTP) was completed, using innovative palynological paleoaltimetry-TP/TPAP [(Tsuga% + Podocarpus%) / (Tsuga% + Podocarpus% + Abies% + Picea%)] ratios, which revealed a rapid uplift of the NTP from low to high elevations during the late Middle Miocene. Here, we analyzed the Ebotu Fauna pollen record (13–12 Ma) from the Hongyazi Basin, situated within the Qilian Mountains, to directly infer the paleoelevation of this region. The pollen assemblages were predominantly composed of conifers (average of 64.0 %), including Picea, Cedrus, and Pinus of the Pinaceae, as well as Cupressaceae, with broadleaves and steppes taxa each accounting for <15 %. This pollen composition evidently reflects a vegetation type dominated by high-mountain conifers forest, consistent with Middle Miocene pollen assemblages from the Qaidam Basin. Application TP/TPAP ratios yielded a paleomidrange of 3492 ± 87 m at 13–12 Ma. Combined with the known elevation of the Qaidam Basin during this period (1885 ± 566 m), the elevation of the Qilian Mountains was calculated to be 4338 ± 653 m. In turn, an elevation of 2646 ± 740 m was obtained for the Hongyazi Basin. This high-elevation terrain provides evidence to support the multi-stage convective removal model of the TP caused by crustal shortening and thickening. It also led to the formation of a humid ecosystem dominated by conifers forest in the Qilian Mountains, supporting the diversification of mammalian taxa.

中文翻译：

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高海拔祁连山及其对中新世晚期构造和生物多样性的启发


祁连山的准确古海拔重建对于促进我们理解青藏高原 （TP） 隆起模型的完整性、其深层结构机制以及与气候、环境和生物多样性变化的相应联系至关重要。最近，使用创新的古生物学古测时法-TP/TPAP [（Tsuga% + Podocarpus%） / （Tsuga% + Podocarpus% + Abies% + Picea%）] 比率完成了对青藏高原北部古中段 （即盆地和山脉的平均海拔） 的首次定量重建，揭示了中新世晚期 NTP 从低海拔到高海拔的快速隆升。在这里，我们分析了位于祁连山脉内的洪崖子盆地的 Ebotu 动物花粉记录（13-12 马），以直接推断该地区的古海拔。花粉组合主要由针叶树组成 （平均 64.0 %），包括松科的云杉、雪橇和松树，以及柏科植物，阔叶树和草原类群各占 <15 %。这种花粉组成显然反映了以高山针叶林为主的植被类型，与柴达木盆地的中新世花粉组合一致。应用 TP/TPAP 比率在 13-12 马 处产生 3492 ± 87 m 的古中距。结合这一时期柴达木盆地的已知海拔（1885 ± 566 m），计算出祁连山的海拔为 4338 ± 653 m。反过来，洪崖子盆地获得了 2646 ± 740 m 的海拔。这种高海拔地形为支持由地壳缩短和增厚引起的 TP 多阶段对流移除模型提供了证据。 它还导致了祁连山以针叶林为主的潮湿生态系统的形成，支持了哺乳动物分类群的多样化。