Abstract
Interbasin arches between hydrographic systems have a heterogeneous geological origin, forming under the influence of several different geomorphological processes. Independent of the underlying processes, these arches compartmentalize present-day river basins, encompassing different water chemistries, habitat types, soil domains, potential energy and, on a geological/evolutionary time scale, aquatic life varieties in the ecosystem. Through most of its length, the water divide between the Amazonian, Paraná-Paraguay, and São Francisco river basins in central South America coincides with an Upper Cretaceous intracontinental igneous alkaline province. This magmatism, independent of its nature, caused intense crustal uplift and influenced hydrological networks at different scales: from continental-scale crustal doming to continental break-up, and finally to local-scale phenomena. The available ages for alkaline rocks indicate a well-defined time-interval between 72.4 to 91 Ma (concentrated between 76 and 88 Ma) period of uplift that contributed to large-scale drainage compartmentalization in the region. Here we show that uplift associated with intrusive magmatism explains the origin and maintenance of the divide between the Amazonian, Paraná-Paraguay, and São Francisco river basins.
Highlights
The age of a river system is a concept that is elusive in fluvial geology[1]
While the geomorphological impact of intracontinental magmatism has not been considered previously, paleodrainage reconstructions have been conducted for the convergent South American continental margin, showing well-supported geological evidence of Miocene marine incursions[5,6], mega-wetlands[7], and other fluvial systems associated with the Andean foreland[8,9,10,11]
The headwater streams of these continental-scale river systems are located at the margins of major South American cratons, namely the Amazonian, São Francisco, Rio de la Plata, São Luiz, and Luiz Alves cratons, which are surrounded by large ancient orogenic belts (Mantiqueira and Tocantins provinces) formed during the amalgamation of the Western Gondwana supercontinent in the Neoproterozoic[16]
Summary
The age of a river system is a concept that is elusive in fluvial geology[1]. Theories regarding the age and existence of river systems include the following. (1) A river is at least as old as the onshore or offshore deposits that are related to it, such as delta or submarine fan deposits or a major erosional feature such as a submarine canyon. (2) A river is at least as old as the last major marine regression from its watershed. (3) The origin of a river can be dated back to the last major tectonic, glacial, and volcanic events affecting its drainage system[1]. The origin of present-day limits of major drainage basins could be influenced by regional uplift in parts of South America during the late Cretaceous, as proposed by recent studies, which was related to the rapid spreading rates in South Atlantic[3].
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