The Himalayan mountain range is one of Earth’s most impressive physical features. For decades scientists have investigated and debated the details of the Himalayas’ origin and evolution as a product of the collision between the Indian and Asian continental plates. One of the many methods of examining how the Himalayas evolved is to study the record of ancient drainage patterns recorded in the sedimentary rocks the range produced as it eroded. The ancient drainage patterns reflect the structural development of the Himalayas and also provide insights about the character and distribution of the neighboring environments that animals and plants inhabited.

Our study examined sandstones deposited roughly 30 million to 18 million years ago (during the Oligocene and Miocene epochs) by Himalayan rivers and coastal channels at Zinda Pir Dome in western Pakistan. We collected data for the flow-direction of water indicated by the orientation of features in the rocks, an approach called paleocurrent analysis. A history of Himalayan drainage in the Zinda Pir Dome area was then constructed from the sequential directions of paleocurrents through layers of the two rock units, the Chitarwata Formation and the Vihowa Formation.

This study is important for several reasons. First, it documents the timing and character of the Indus River’s dramatic drainage shift from the Katawaz Basin towards its current position in the Himalayan foreland basin about 19.5 million years ago. Second, this study provides a plausible paleogeographic explanation for why the ancient environments and faunas vary between the important Zinda Pir Dome and Dera Bugti fossil localities. Finally, this work provides a geographic model for the western Himalayan region during the Oligocene that can be tested through future analysis of sandstone composition at Dera Bugti and Zinda Pir Dome and through additional fossil collection in the Katawaz Basin.