Geological and sedimentary evidence indicates that the major river systems of South Asia, including the precursors to the modern Ganges-Brahmaputra network, originated or underwent major establishment during the Miocene epoch.
Papers [0] and [4] provide explicit chronological and sedimentary evidence regarding the initiation and evolution of major South Asian and Himalayan river systems during the Early Miocene. The rest of the papers do not directly address the origin timing of the Ganges River system. Therefore, the claim is supported.