Abstract This research provides geomorphological and sedimentary data on the Salado-Juramento fluvial megafan, the second largest megafan (204,747 km2) of the Chaco aggradational plain, generated by the Salado-Juramento River in NE Argentina. It comprises one of the most extensive depositional systems of the Central Andean foreland basin system in South America, also being among the largest megafans on Earth. Despite this, it has not been previously studied from the perspective of its geomorphology, stratigraphy and dynamic evolution. An integrated approach focusing on the analysis of morpho-sedimentary processes, the resulting landforms and the reconstruction of the Late Quaternary evolution is presented here. The applied methods combine geomorphological mapping from remote sensing images analysis, assessment of landforms and processes, and field data. Historical documents were also analysed. Insights into the near sub-surface stratigraphy were obtained from analysis of research boreholes (up to 30 m depth), integrated with groundwater borehole information. The Fluvial Megafan of the Salado-Juramento Geomophological System comprises four geomorphological units: 1) the middle-proximal area of the megafan, 2) the distal area of the megafan, 3) the complex fluvio-aeolian belt of the Golondrinas-Calchaqui, and 4) the present fluvial belt of the Salado. Thirteen geomorphological sub-units were defined and mapped, representing the complexity of sub-environment interactions. Amalgamated braided channel deposits and aggradation lobes with limited floodplain muds are common in the proximal area, while mixed-load, low-energy, narrow, shallow, and sinuous palaeochannels and associated floodplain marsh deposits characterize the distal area, with groundwater discharges and hydromorphic soils. The megafan construction was dominated by short-term sedimentation and channel avulsions to overbank areas. Fan-shaped depositional lobes of the proximal area and sandy channel deposits and sand sheets linked to terminal splays that are covering mud-flat deposits (floodplains, including palaeosols) in the middle area suggest a high-flow regime. Neotectonics favoured subsidence, avulsion, and prolonged flooding events, with high potential of preservation of an extensive Late Quaternary wetland unit, ponds, lakes, soils, and loessic deposits in the distal megafan. Aggradation and progradation patterns have been conditioned by tectonic control regulating the interaction between the megafan and its axial trunk river (Parana). Furthermore, the Late Quaternary megafan sequences would also have responded to climatic changes, primarily related to strong hydroclimatic seasonality linked to changes in the South American monsoon system strength. Seasonal high sediment load of the formative river linked to the characteristics of the Andean basin (38,000 km2) and its climatic patterns are considered as the main control on megafan dynamics over at least the Upper Quaternary. Morpho-stratigraphical data of the megafan presented here and the first interpretation of its Quaternary evolution is the key to support socio-economic decisions on aquifer exploitation, land uses, and infrastructure planning.

中文翻译：

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SALADO/Juramento Fluvial MegaFan，中部安第斯前陆盆地（阿根廷查科平原）的地貌和晚第四纪沉积记录

摘要 本研究提供了 Salado-Juramento 河流巨型扇的地貌和沉积数据，该巨型扇是由阿根廷东北部 Salado-Juramento 河生成的 Chaco 积聚平原的第二大巨型扇（204,747 平方公里）。它包括南美洲中部安第斯前陆盆地系统中最广泛的沉积系统之一，也是地球上最大的巨型扇之一。尽管如此，以前还没有从地貌、地层和动力演化的角度对其进行研究。本文提出了一种综合方法，重点是对形态沉积过程、由此产生的地貌和晚第四纪演化重建的分析。应用的方法结合了遥感图像分析的地貌制图，地貌和过程的评估，和现场数据。还分析了历史文献。通过对研究钻孔（最深 30 m）的分析与地下水钻孔信息相结合，获得了对近地下地层的深入了解。Salado-Juramento 地貌系统的河流大扇由四个地貌单元组成：1) 大扇的中近端区域，2) 大扇的远端区域，3) Golondrinas-Calchaqui 复杂的河流-风成带，以及4）目前的萨拉多河带。定义并绘制了 13 个地貌亚单元，代表了亚环境相互作用的复杂性。近端地区常见混合辫状河道沉积物和具有有限泛滥平原泥浆的加积裂片，而混合负载、低能量、窄、浅、蜿蜒的古河道和相关的漫滩沼泽沉积是远端地区的特征，有地下水排放和水形土壤。巨型风扇的建造主要是短期沉积和河道侵蚀到河上地区。近端区域的扇形沉积裂片和与覆盖在中部区域的泥滩沉积物（泛滥平原，包括古土壤）的末端裂隙相连的砂质通道沉积物和砂板表明存在高流量状态。新构造有利于沉降、剥脱和长期洪水事件，具有保存大范围的晚第四纪湿地单元、池塘、湖泊、土壤和远端巨型扇中的黄土沉积物的潜力。加积和进积模式受构造控制的影响，该控制调节了巨型扇及其轴向干河（巴拉那）之间的相互作用。此外，晚第四纪巨型扇序列也会对气候变化做出反应，主要与与南美季风系统强度变化相关的强烈水文气候季节性有关。与安第斯盆地 (38,000 平方公里) 的特征及其气候模式相关的形成性河流的季节性高泥沙负荷被认为是至少在上第四纪对巨型风扇动力学的主要控制。此处提供的巨型扇形地层数据及其第四纪演化的第一个解释是支持有关含水层开发、土地利用和基础设施规划的社会经济决策的关键。此外，晚第四纪巨型扇序列也会对气候变化做出反应，主要与与南美季风系统强度变化相关的强烈水文气候季节性有关。与安第斯盆地 (38,000 平方公里) 的特征及其气候模式相关的形成性河流的季节性高泥沙负荷被认为是至少在上第四纪对巨型风扇动力学的主要控制。此处提供的巨型扇形地层数据及其第四纪演化的第一个解释是支持有关含水层开发、土地利用和基础设施规划的社会经济决策的关键。此外，晚第四纪巨型扇序列也会对气候变化做出反应，主要与与南美季风系统强度变化相关的强烈水文气候季节性有关。与安第斯盆地 (38,000 平方公里) 的特征及其气候模式相关的形成性河流的季节性高泥沙负荷被认为是至少在上第四纪对巨型风扇动力学的主要控制。此处提供的巨型扇形地层数据及其第四纪演化的第一个解释是支持有关含水层开发、土地利用和基础设施规划的社会经济决策的关键。主要与与南美季风系统强度变化相关的强烈水文气候季节性有关。与安第斯盆地 (38,000 平方公里) 的特征及其气候模式相关的形成性河流的季节性高泥沙负荷被认为是至少在上第四纪对巨型风扇动力学的主要控制。此处提供的巨型扇形地层数据及其第四纪演化的第一个解释是支持有关含水层开发、土地利用和基础设施规划的社会经济决策的关键。主要与与南美季风系统强度变化相关的强烈水文气候季节性有关。与安第斯盆地 (38,000 平方公里) 的特征及其气候模式相关的形成性河流的季节性高泥沙负荷被认为是至少在上第四纪对巨型风扇动力学的主要控制。此处提供的巨型扇形地层数据及其第四纪演化的第一个解释是支持有关含水层开发、土地利用和基础设施规划的社会经济决策的关键。