The mega-river functions differently from ordinary rivers and its floodplain is characterized by its magnitude, morphological complexity, and evolutionary history. This study analyzes the morphological and evolutionary characteristics of the Upper Paraná mega-river floodplain (Qm 13,000 m³ s⁻¹), characterizing it as polygenetic owing to the various formative processes involved, many of which are no longer active and have extended since the end of the Pleistocene. The Upper Paraná floodplain is adjacent to the channel and in-channel on the large islands of its lower section. The 235 km study reach river has anabranching stretches that are separated by nodal sections. The analysis used satellite images, aerial photographs, 35 colors, and 52 absolute dates. Four types of floodplains were characterized: inherited, formed by processes and morphologies no longer active in the system; bayfill, formed by overflow deposits in flooded areas; crest-and-trough, by the annexation of lateral bars; and mixed, by the combination of the types above and association of the Paraná floodplain with its tributaries. Floodplain formation occurred in three phases. 1) At the end of the Pleistocene when the river developed a braided sand-gravel pattern under a dry climate. 2) It began at the Pleistocene-Holocene limit, when climatic improvement produced hydrological changes in the river leading to the vertical and lateral excavation of the old floodplain, generating a new channel and a sandy terrace 10 m above the current river level. The formation of the current floodplain began in this phase with the abandonment of the pioneer lake-islands. 3) It started with a small semi-arid event in the mid-Holocene until the present. The current floodplain and river hydrology were defined in this phase. Tectonic interventions for forming the floodplain are also addressed in the text. Considering its varied origin, the floodplain is polygenetic, implying a complex mosaic of environments whose connectivity relationships are still unknown. We believe that the concept of polygenetic floodplains presented in this study will help the understanding of hydrological and ecological functioning of the polygenetic floodplains of tropical mega-rivers.

特大河流的功能不同于普通河流，其洪泛区的特点是规模、形态复杂性和演化历史。本研究分析了巴拉那河上游泛滥平原（Qm 13,000 m ³  s ^{-1 ）的形态和演化特征}），由于涉及的各种形成过程，将其表征为多基因的，其中许多不再活跃并且自更新世末期以来已经延伸。上巴拉那河漫滩在其下部的大岛上与河道和河道内相邻。这条 235 公里长的研究河段有一条分叉的河段，由节点部分隔开。该分析使用了卫星图像、航拍照片、35 种颜色和 52 个绝对日期。四种类型的洪泛区被表征：遗传，由系统中不再活跃的过程和形态形成；填海区，由洪水区域的溢流沉积物形成；波峰和波谷，由侧钢筋的兼并；和混合，通过上述类型的组合以及巴拉那洪泛区与其支流的关联。泛滥平原的形成分三个阶段发生。1）在更新世末期，河流在干燥的气候下形成辫状砂砾石格局。2) 它始于更新世-全新世界限，当时气候改善导致河流水文变化，导致旧洪泛区纵向和横向开挖，形成新河道和高于当前河流水位 10 m 的沙质阶地。当前洪泛区的形成始于这一阶段，最初的湖岛被废弃。3）它始于全新世中期的一次小型半干旱事件，直到现在。目前的洪泛区和 当气候改善导致河流的水文变化导致旧洪泛区的垂直和横向开挖，在当前河流水位以上 10 m 处形成新的河道和沙质梯田。当前洪泛区的形成始于这一阶段，最初的湖岛被废弃。3）它始于全新世中期的一次小型半干旱事件，直到现在。目前的洪泛区和 当气候改善导致河流的水文变化导致旧洪泛区的垂直和横向开挖，在当前河流水位以上 10 m 处形成新的河道和沙质梯田。当前洪泛区的形成始于这一阶段，最初的湖岛被废弃。3）它始于全新世中期的一次小型半干旱事件，直到现在。目前的洪泛区和河流水文是在这一阶段定义的。文中还讨论了形成洪泛区的构造干预措施。考虑到其不同的起源，洪泛区是多基因的，这意味着环境的复杂镶嵌，其连接关系仍然未知。我们相信，本研究中提出的多成因洪泛区概念将有助于理解热带大河流多成因洪泛区的水文和生态功能。