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首页> 外文期刊>Journal of Palaeogeography >Palaeogeography, palaeohydraulics and palaeoclimate of the Mio–Pliocene Siwalik Group, eastern India
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Palaeogeography, palaeohydraulics and palaeoclimate of the Mio–Pliocene Siwalik Group, eastern India

机译：印度东部Mio-Pliocene Siwalik组的古地理，古水力和古气候

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Abstract South–southwestward palaeocurrent swerved to east–southeast and then broadly to southeast over the transition from alluvial fan to axial channel and then to the flood plain in the Mio–Pliocene foreland system within which the Siwalik Group depositd in Darjeeling-Jalpaiguri Districts, eastern India. Palaeocurrent pattern is found to be multi-modal on the fans, virtually unimodal on the axial channel zone and again multi-modal, more profoundly, on the flood plain. Coarse siliciclastic mass-flows were progressively eliminated and gave way to predominant bed-load transport downfan and the axial river, and then to suspension-load dominance in fine siliciclastics on the flood plain. Distal flood plain lacustrine sediment included most of the coals and the entire bulk of the dolomitic limestone. Further resolution in palaeogeography within the frame of aforementioned foursome facies associations is elicited in twenty-six distinctive facies altogether. Critical evaluation of chemical indices (CIA, CIW, ICV, PIA, as well as Rb/Sr ratio) for weathering and depleted δ18O values indicate a high precipitation rate. The contention is further corroborated by the high discharge rate calculated from cross-set thicknesses within the main channel deposits. Reconciliation of various relevant data sets collected or calculated from all known worksites along the entire 2000 km-long exposure belt of the Siwaliks along the Himalayan foothills reveal confluence of two tributaries, one from the west and the other from the east, close to the present study area before escaping onto the Indian plains. Channel parameters, channel-belt width and discharge thus attained maxima in the present study area. The precipitation rate and temperature increased eastward overall as a prelude to the modern trend in this regard. 13C enrichment indicates that the transition from {C3} to {C4} vegetation had already set in.
机译：摘要从冲积扇向轴向河道过渡，然后到密欧-上新世前陆系统的洪泛平原，西南-西南古水流先后向东-东南，然后大范围向东南倾斜，其中Siwalik群沉积在东部的大吉岭-贾尔派古里地区印度。人们发现，古风流在风机上是多峰的，在轴向河道带几乎是单峰的，而在泛洪平原上又是多峰的。渐渐消除了粗碎屑碎屑岩的质量流，并让位于主要的床荷输运向下的风机和轴向河，然后变成了洪泛平原上细碎碎屑岩的悬浮荷重优势。洪水泛滥的湖相沉积物包括大部分的煤和白云质石灰岩的全部。在上述四性相关联的框架内，在古地理学中得到了进一步的解决，共计有26个独特的相。严格评估化学指数（CIA，CIW，ICV，PIA以及Rb / Sr比）和老化的δ18O值表明了高的降水率。根据主通道沉积物内的交叉设定厚度计算出的高放电速率进一步证实了这一争执。沿着喜马拉雅山麓的西瓦利克整个2000公里长暴露带，从所有已知工地收集或计算的各种相关数据集进行核对，揭示了两个支流的汇合点，其中一个来自西方，另一个来自东方。研究区，然后逃到印度平原。因此，在本研究区中，河道参数，河道带宽度和排放量达到了最大值。降水率和温度总体上向东升高，这是这方面现代趋势的前奏。 13C富集表明从{C3}到{C4}的植被过渡已经开始。

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