An Autogenic Cycle of Fluvial Transience in Dipping, Layered Rocks

We describe an autogenic process by which steady fluvial incision through dipping, layered rocks of different erodibilities cyclically generates migrating drainage divides. We develop an analytical expression for calculating the autogenic periodicity, test it by simulating the incision of idealized strike valleys with a landscape evolution model, and apply our models to estimate the autogenic periodicity within two strike valleys in central Utah. Our analysis suggests that depending on the long-term incision rate of the San Rafael River network, the autogenic periodicity within the two valleys can overlap with the similar to 100 kyr glacial-interglacial period of climatic forcing, in which case the two different signals would be difficult to separate. Our method should apply to other regions of dipping layered rocks and can be used as a preliminary test to assess whether autogenic or exogenic forcings are more likely to have created a given set of transient features. Plain Language Summary Climate change, tectonics, and human activity sometimes create short-lived topographic features called transient landforms. Geomorphologists use transient landforms to understand how factors like ancient earthquakes or changes in the amount of rainfall interact with Earth's surface. However, sometimes transient landforms are created spontaneously without any of these forces, and we call the processes that cause this to happen autogenic processes. In this study, we focus on transient landforms called mobile drainage divides (boundaries between river basins that move over time). Previous studies mapped mobile drainage divides in central Utah and suggested that they were created by climate change thousands of years ago. Instead, we hypothesize that they may have been created by an autogenic process that occurs when rivers erode through multiple varieties of layered rocks. We analyze the factors that control this process and model it using a specialized computer code. The results confirm that the mobile drainage divides in central Utah could have been created by the autogenic process, and so the original interpretation that they were created by past climate change may not be correct. Our analysis has important implications for future studies that try to understand how climate change or tectonics interact to shape Earth's surface.

Automated summary

An autogenic process of steady fluvial incision through different erodibility layered rocks cyclically generates migrating drainage divides, with potential overlap between the autogenic periodicity and the glacial-interglacial period of climatic forcing in central Utah. This suggests a need for further research to distinguish between autogenic and exogenic forces creating transient landforms.