The final stages of evolution of the Himalayan foreland basin (HFB) are preserved in the Siwalik Group of rocks deposited by meandering and/or braided rivers in the western and central regions of HFB. However, the time-equivalent deposits in the eastern part of the foreland provide contradictory evidence of both terrestrial and marine environments. To address the ambiguity, molecular level characterization and stable isotopic composition of organic matter (OM) have been employed in the late Miocene-Pliocene sequence of the eastern HFB. The n-alkane distribution, carbon isotopic (δ¹³C) signature of n-alkanes and distribution of hopane and sterane isomers suggest OM contributions from both marine and terrestrial sources during the late Miocene period. Increase in short-chain n-alkane abundance and gammacerane index, low pristane/phytane ratio, higher δ¹³C values, higher regular sterane/17α-hopane, C₃₁R/C₃₀-hopane and C₂₇/C₂₉ steranes ratios and presence of C₃₀ sterane provides substantial evidence of stratified anoxic conditions and marine influences at specific stratigraphic intervals. During the late Miocene period, mixing of marine OM sources with terrestrial sources argue for marginal marine depositional conditions amid fluvial-dominating environments. The entry of marine waters in the eastern HFB through the pre-existing cratonic troughs possibly resulted from eustatic or relative sea-level rise. No further evidence of marine incursions is observed in the younger Pliocene sediments. The higher detrital influx from the rising Himalayas, the onset of Northern Hemisphere Glaciation and evolution of physical barriers such as Shillong Massifs and Barind Tracts altogether led to the cessation of marine incursions into the HFB.

中文翻译：

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喜马拉雅前陆盆地充填阶段海洋入侵的生物标志物和碳同位素证据

喜马拉雅前陆盆地（HFB）演化的最后阶段保存在HFB西部和中部蜿蜒和/或辫状河沉积的Siwalik组岩石中。但是，前陆东部的时间等价沉积物为陆地和海洋环境提供了相互矛盾的证据。为了解决歧义问题，东部HFB的中新世-上新世序列已采用了分子水平表征和稳定的有机物质同位素组成（OM）。所述Ñ烷烃分布，碳同位素（δ ¹³ C）的签名Ñ-烷烃和hop烷和甾烷异构体的分布表明，在中新世晚期，海洋和陆地来源的OM贡献很大。增加短链Ñ烷烃丰度和伽马蜡指数，低姥鲛烷/植比，较高的δ ¹³ C值，更高的规则甾烷/17α-藿，C ₃₁ R / C ₃₀ -hopane和C ₂₇ / C ₂₉甾烷比和存在C ₃₀甾烷为特定的地层间隔提供了分层缺氧条件和海洋影响的重要证据。在中新世晚期，海洋潮汐源与地面源的混合表明在河流主导的环境中边缘海洋沉积条件存在。HFB东部海域通过先前存在的克拉通海槽进入海域可能是由于水位上升或相对海平面上升所致。在上新世较年轻的沉积物中未观察到海洋入侵的进一步证据。喜马拉雅山脉上升，北半球冰河的爆发以及西隆断层块和巴林道等物理屏障的演变，导致更多的碎屑涌入，导致停止了对HFB的海上入侵。