How Two Different Cenozoic Geologic and Glacial History Paradigms Explain the Southcentral Montana Musselshell-Yellowstone River Drainage Divide Origin, USA

Abstract

The accepted Cenozoic geologic and glacial history paradigm (accepted paradigm) considers the southcentral Montana Musselshell-Yellowstone River drainage divide to have originated during Tertiary (or preglacial) time while a new and different Cenozoic geologic and glacial history paradigm (new paradigm) describes how headward erosion of a northeast-oriented Musselshell River valley segment captured huge southeast-oriented meltwater floods to create the drainage divide late during a continental ice sheet’s melt history. Northwest to southeast oriented divide crossings (low points observed on detailed topographic maps where water once flowed across the drainage divide), southeast-oriented Yellowstone and Musselshell River segments immediately upstream from northeast-oriented Yellowstone and Musselshell River segments, and southeast- and northwest-oriented tributaries to northeast-oriented Yellowstone and Musselshell River segments indicate a major southeast-oriented drainage system predated the northeast-oriented Yellowstone and Musselshell River segments. Closeness of the divide crossings, divide crossing floor elevations, large escarpment-surrounded erosional amphitheater-shaped basins, and unusual flat-floored internally drained basin areas (straddling the drainage divide), all suggest the previous southeast-oriented drainage system moved large quantities of water which deeply eroded the region. In the mid-20th century geomorphologists working from the accepted paradigm perspective determined trying to explain such erosional landform evidence from the accepted paradigm perspective was a nonproductive research activity and now rarely investigate erosional landform origins. On the other hand, the new paradigm appears to explain most, if not all observed erosional landform features, although the two paradigms lead to significantly different regional Cenozoic geologic and glacial histories that cannot be easily compared.