Coupling geo- and bio-chronometers to reconstruct river histories: evolution of the Douro River, Portugal
Dr. Steven Binnie
Geology and and Mineralogy
Idea
River networks evolve in response to changes in their surrounding environments and so fluvial histories tell us about past landscape defining events. Topographic evidence in the landscape showing that rivers have adjusted to new boundary conditions takes the form of geomorphic features, such as fluvial terraces (Pazzaglia, 2013). We can date these terraces with cosmogenic nuclides to constrain the timing and rates of fluvial evolution, and over the last decade, or so, more sophisticated approaches for such dating have been developed (e.g. Erdlanger et al., 2012). On the other hand, what has been significantly underappreciated by the geomorphology community is how the biological record of the aquatic species that inhabit these rivers can inform us of fluvial histories (Craw et al., 2008). The phylogenetic records of riverine species, such as amphipods (shrimp), can be analyzed using molecular clock dating to show when fluvial networks reorganized. Combining cosmogenic nuclide with molecular clock dating thus has great potential for understanding, amongst other things, the relationships between fluvial evolution and the major climatic changes during the Quaternary.
Recognizing this potential during the multidisciplinary CRC1211 project, combining geoscience and biology, Dr Binnie and Dr Kathrin Lampert (of the Inst. of Zoology at UoC) have achieved initial success, integrating these techniques to understand biological and landscape evolution in the Atacama Desert. This IMfESS proposal now seeks to expand on this success by testing the geo- bio-chronology approach outside of deserts, specifically in the Douro River, draining the largest catchment of the Iberian Peninsula. Here it is known that upstream portions of the river were once endorheic, but began to drain into the Atlantic following a major drainage capture event. The age of this event is poorly constrained and based on extrapolation it is suggested to have occurred between ~ 3.7 - 1.8 Ma (Cunha et al., 2019). The main hypothesis of this project is that the timing of Douro River reorganization derived from molecular clock dating of amphipods will be coeval with the start of incision obtained by cosmogenic nuclide dating of the river’s highest terrace. It is further hypothesed that this timing will relate to a period of major global climatic change. If successful, this study would serve as a pilot for a larger DFG research grant proposal, aimed at studying in more detail the coupling of these complimentary dating techniques at other locations worldwide.
Plan
The uppermost terrace of the downstream reach of the Douro River in central Portugal will be sampled for cosmogenic nuclide analysis. Human modification of the terrace surface precludes exposure dating and instead isochron burial dating will be used. This requires several samples to be dug from depths in excess of ~3 m and their 10Be and 26Al concentrations measured by accelerator mass spectrometry at CologneAMS. Amphipod samples would be collected from the main stem and several side tributaries of the Duoro River in Portugal and Spain and undergo molecular analysis of mitochondrial genes (COI) by Dr Lampert. Previous fieldwork in this area has built good relations with Portuguese colleagues, who would help facilitate sample collection, in particular obtaining permission and arranging the digging to get cosmogenic nuclide samples from depth.
Status
The project fieldwork in Portugal happened in late May 25.