Collaborative Research: Reevaluating the Timing and Driver of Escarpment Retreat in Southeast Australia

Escarpments are steep slopes that extend for hundreds of miles and separate two relatively flat areas, one along the coast of a continent and the other further inland. Escarpments are found along the edges of many continents that separated from another continent millions of years ago due to plate tectonics. If escarpments form when the continents separate, scientists do not understand how present-day escarpments reach their locations and then remain prominent features of landscapes for so long. Additionally, some scientists think escarpment formation occurs more recently, unrelated to the continents separating. The researchers will investigate when the Great Escarpment in southeast Australia formed and how quickly it reached its present-day location. They will do this using both information about past erosion rates recorded in rocks around the escarpment and computer models that can mimic the process of an escarpment forming and retreating. The new data and models generated for this project will help in understanding the origin of escarpments around the world. This project supports 2 early career women PIs, graduate and undergraduate education, and outreach to K-12 through an established video series supported curriculum that is designed to support K-12 learning. This project aims to place new constraints on the timing of escarpment retreat in southeast Australia, with the broader goal of reevaluating the cause of escarpment formation and retreat. The southeast Australian escarpment is often linked with continental rifting beginning ca. 100-85 Ma. Recent models and observations, however, raise questions about the timing and therefore origin of escarpment formation. To discriminate between escarpment origin hypotheses, the researchers will collect apatite 4He/3He datasets from a bedrock sample transect perpendicular to the southeast Australian escarpment, which will record the modest amounts of exhumation predicted by landscape evolution models during escarpment retreat. They will use the apatite 4He/3He constraints on the timing and magnitude of cooling to inform new, paired landscape evolution and thermo-kinematic models. This will enable them to reevaluate a nearly half-century old paradigm about the geomorphic evolution of southeast Australia. In doing so, they will develop a more robust understanding of how continental rifting shapes the long-term topographic evolution of passive margins, and of the importance of other factors like mantle thermal conditions in driving rock uplift and escarpment formation. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.