The Himalayan foreland basin and other parts of the world had witnessed a dramatic change in the ecological structure during the Late Miocene, as indicated by the increase in abundance of C₄ plants in a C₃ dominated ecosystem. However, the asynchronous expansion of C₄ plants across the latitudes, as well as within the different sub-basins of the Himalayan foreland basin, tentatively suggests that regional climatic factors and sedimentary architecture vis-à-vis geomorphological settings might have an important influence in controlling the abundance of C₄ plants. This study has carried out sedimentological and palaeohydrological analyses of the Siwalik channels at Naladkhad and Ranital regions of the Kangra sub-basin, north-west Himalaya, and estimated slope and sinuosity of the modern Himalayan fan rivers (n > 100), which provides a hydrological analogue for the Siwalik channels. The results suggest that the Siwalik Group in the Kangra sub-basin was deposited by braided rivers, situated at the proximal part of palaeo-alluvial fan. In addition to climate-driven changes, the comparison between sedimentary architecture and published carbon isotope data from the Kangra sub-basin suggests that channel-fill dominated fan-proximal Naladkhad and Ranital regions favoured the growth of C₃ plants until ca 6 Ma, a time when Pakistan Siwaliks were dominated by C₄ plants. In comparison to the Kangra sub-basin, Pakistan Siwaliks are characterized by a higher abundance of floodplain sediments and possibly represent a distal fan deposit. Data from other parts of the world similarly suggest that, in addition to climate forcing, the dominance of overbank fines favoured the growth of C₄ plants. Therefore, detailed knowledge of the depositional environment and palaeo-geomorphic setting of the sedimentary archives is essential to understand the influence of sedimentary architecture on the spatio-temporal variation in the abundance of C₄ vegetation, especially for foreland basin settings, where lateral facies transition rate is high.

中文翻译：

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重新审视喜马拉雅前陆和全球其他地区 C3 到 C4 植物的历时过渡：沉积学视角

喜马拉雅前陆盆地和世界其他地区在晚中新世期间见证了生态结构的巨大变化，这表现为以 C ₃为主的生态系统中 C ₄植物丰度的增加。然而，C ₄植物跨纬度以及喜马拉雅前陆盆地不同子盆地内的异步扩张，初步表明区域气候因素和沉积结构相对于地貌环境可能具有重要影响。控制 C ₄的丰度植物。本研究对喜马拉雅西北部康格拉亚盆地 Naladkhad 和 Ranital 地区的 Siwalik 河道进行了沉积学和古水文分析，并估算了现代喜马拉雅扇河流 ( n  > 100) 的坡度和曲折度，提供了Siwalik 河道的水文模拟。结果表明，Kangra 亚盆地的Siwalik 群由辫状河沉积，位于古冲积扇近端。除了气候驱动的变化之外，沉积结构与来自 Kangra 子盆地的已发表碳同位素数据之间的比较表明，通道填充主导的扇近侧 Naladkhad 和 Ranital 地区有利于 C ₃植物的生长，直到大约6 Ma，当时巴基斯坦 Siwaliks 以 C ₄植物为主。与 Kangra 子盆地相比，巴基斯坦 Siwaliks 的特点是洪泛区沉积物丰度更高，并且可能代表了远端扇形沉积物。来自世界其他地区的数据同样表明，除了气候强迫之外，过度银行罚款的主导地位有利于 C ₄植物的生长。因此，详细了解沉积档案的沉积环境和古地貌环境对于了解沉积结构对 C ₄植被丰度时空变化的影响至关重要，尤其是对于侧相过渡的前陆盆地环境。率很高。