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首页> 外文期刊>Journal of geodynamics >The Lower Siwalik foreland basin sedimentation in the Kumaun Himalaya (India): A transition from megafan setting to incised valley fills
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The Lower Siwalik foreland basin sedimentation in the Kumaun Himalaya (India): A transition from megafan setting to incised valley fills

机译：印度库玛恩喜马拉雅山的下西瓦里克前陆盆地沉积：从巨型扇形过渡到切开的河谷填充物的过渡

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摘要

About 300-900 m thick the Lower Siwalik Subgroup exposed in the Kumaun Himalaya has been studied along three far spaced sections, which show variable stratigraphic changes in sedimentation pattern. Available magnetostratigraphic dates in the Kathgodam Ranibagh section indicate Late Miocene age (12-10Ma) of the Lower Siwalik Subgroup. Detailed lithofacies analysis reveals four depositional settings namely, the Sandstone Lithofacies Association (Channel deposits), the Mudstone Lithofacies Association (Floodplain deposits), the Mottled Mudstone Lithofacies Association (Distal floodplain palaeosols), and the Mottled Siltstone Lithofacies Association (Interfluve deposits). Based on available data on channel pattern, lithofacies association, palaeocurrent pattern, and petrography, stratigraphic cyclicity is analyzed. The complete group is interpreted to be deposited in two Megacycles A and B. About 500 m thick, coarsening upward Megacycle A is internally made up of two Lithofacies sucessions I and II. The cycle is made up of meandering and anastomosing rivers towards the base (Lithofacies Succession I) that gradually evolves into braided rivers towards top (Lithofacies Succession II). This megacycle is inferred as prograding megafan deposit.In contrast, about 400 m thick Megacycle B, made up of two Lithofacies successions III and IV, is fining upward. This cycle is made up of thickly developed meandering braided river systems at base interbedded with thick interfluve and distal flood plain deposits (Lithofacies Succession III) that gradually becomes thinner towards top, and river system changes to predominantly meandering type (Lithofacies Succession IV). The Megacycle 13 is inferred to be deposited in tectonically active basin, characterized by incision of rivers.
机译：沿三个间隔较远的断层研究了暴露在库玛恩喜马拉雅山中的下西瓦利克次群约300-900 m厚，这些断层显示出沉积模式的变化地层变化。 Kathgodam Ranibagh部分中可用的地磁日期表明下西瓦里克次组的中新世晚期（12-10Ma）。详细的岩相分析揭示了四个沉积环境，即砂岩岩相协会（河道沉积物），泥岩岩相协会（洪泛区沉积物），斑驳的泥岩岩相协会（远洪泛滥古土壤）和斑驳的粉砂岩岩相协会（穿流沉积物）。根据有关通道模式，岩相联系，古流模式和岩石学的可用数据，分析了地层周期性。完整的组被解释为沉积在两个兆发周期A和B中。约500 m厚，向上变粗的兆发周期A内部由两个岩相接缝I和II组成。该周期由朝向底部（利特霍菲人继承I）的蜿蜒河和吻合河组成，然后逐渐演变成朝向顶部（利特霍菲人继承II）的辫状河。推测该大循环是正在积聚的巨扇沉积物。相比之下，由两个Lithofacies继承III和IV组成的约400 m厚的超级循环B正在向上搜寻。该周期由底部厚厚的蜿蜒辫状辫状河系组成，中间夹杂着厚厚的河道和远洪泛滥平原沉积物（Lithofacies继任III），该沉积物朝顶部逐渐变薄，河流系统转变为曲折型（Lithofacies继任IV）。推测Megacycle 13沉积在构造活跃的盆地中，其特征是河流切割。

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