Dr Victoria Fernandes Honours Projects

Deciphering Lag-times in Alluvial River Terrace Formation

River terraces are ubiquitous geomorphic markers of change, preserving the erosional response of rivers to external forcing such as climate and tectonics. Thus, dating these landforms, often achieved by measuring the accumulation of cosmogenic nuclides on terrace surfaces, is of crucial importance to establish landscape chronologies and better understand and predict landscape responses to forcing. Recent models of terrace development in alluvial rivers reveals that the age of formation of a distinct terrace level may vary along its length, showing different patterns for different external forcings, with time lags of up to half a glacial cycle for rivers >200 km in length (Ruby et al., 2025). However, due to rare preservation of continuous terrace surfaces along full lengths of long rivers, or lack of sufficient age sampling along for statistical analysis, testing such models proves challenging. Yet Río Santa Cruz in Southern Patagonia, Argentina, provides a unique opportunity to test these model predictions. The Patagonian foreland, a semi-arid, low-relief landscape between the Patagonian Andes and the Atlantic Ocean, preserves a rich record of river response to external forcing extending more than 1 Myr into the past. Starting around 7 Ma, glaciers heavily modified source catchments; their advance and retreat have in turn generated variations in sediment delivery to downstream rivers, as well as a flexural isostatic response that extends into pro-glacial regions. At the same time, an opening window in the subducting slab allows warm asthenosphere to upwell and heat the overlying lithosphere, making it particularly susceptible to deformation. The Río Santa Cruz drains from pro-glacial lakes several hundred kilometres eastward across the foreland, preserving numerous levels of fluvial terraces, continuous over 250 km. Exposure ages of river terraces derived from cosmogenic nuclides reveal a prominent terrace level formed throughout the region around 1 Ma, with subsequent terrace levels showing apparent 100-kyr cyclicity, revealing likely dominant climate control (Fernandes et al., 2025).
Although the terrace dating is sufficient to establish a glacial chronology, additional cosmogenic nuclide ages along the length of dated terraces would provide the necessary data to investigate the existence and size of time lags along the preserved terraces.

Project aims:
The aim of this project is to establish a robust along-terrace dating for 6 terraces of the Río Santa Cruz to characterize how the along-terrace age varies for individual terrace levels.

Techniques:
This project involves labwork for the extraction of cosmogenic nucliedes (10Be), measurement of 9Be/10Be ratios, and age calculation for up to 32 rock samples from Southern Patagonia. Statistical analysis of new and existing data, as well as modelling of alluvial rivers will be  required. Note: this project does not have a component of fieldwork.