Sedimentary fluxes in a changing climate: Sensitivity of Pyrenean catchments to the Paleocene-Eocene Thermal Maximum

Climate change impacts sediment routing systems by modifying erosional processes, sediment transfer dynamics, and depositional forms. Understanding the sensitivity of surface processes to hydrological changes accompanying climate perturbations is crucial to predicting sediment dispersal in past and modern sedimentary systems and to read the narrative of climate change history preserved in sedimentary successions.

Increased clastic sedimentation rates in marine basins are observed worldwide during the Paleocene-Eocene Thermal Maximum (PETM, 56 Ma), the most rapid and intense climate change of the Cenozoic, and often postulated to express increased erosion rates in upstream catchments. However, to date, none of the quantitative assessments of sedimentary flux evolution across the PETM are based on closed volumetric budgets, and hence, the sensitivity of erosional catchments to the PETM climate perturbation remains to be established.

The Tremp piggyback basin (South-Central Pyrenean Foreland, Spain), by creating a trap at the foothill of the growing orogen, offers the opportunity to quantify and compare sediment volumes deposited during the Thanetian pre-PETM climate and during the PETM event. Using data from field-measured sections and boreholes from the literature to compute rock volumes corrected for porosity, compaction, and carbonate content, we find a 3.5-fold increase in sediment flux during the PETM in the Tremp Basin.

The sensitivity of erosion to climate change in Pyrenean catchments during the PETM can thus be expressed as an increase in erosion by a factor of 3.5 following a global temperature increase of 5 to 8°C.

However, what are the parameters of climate that have changed during the PETM global warming and are responsible for the increase in erosion: vegetation, mean annual precipitation, frequency-amplitude distribution of rainfall events? To address this question, we explore different precipitation change scenarios using the BQART and Stream Power Law models. With both models, increasing mean annual precipitation by a factor of 1.45 as predicted by climate simulations during the PETM in Northern Spain (Rush et al., 2021), only leads to a minor increase in sediment fluxes by a factor of 1.4, inconsistent with the landscape sensitivity deduced above. Using a more elaborate hydrograph implying a switch to more frequent (by 2 to 10 times) and more intense (by 8.1 times; Chen et al., 2018) precipitation events during the PETM leads to a 2.7-fold increase in sediment flux out of Pyrenean catchments, in better agreement with the observations, i.e. explaining 75% of the response.

This suggests that the erosional response of catchments during the PETM global warming could have been primarily controlled by physical erosion but may also have required the influence of additional sediment production and delivery processes, possibly associated with vegetation changes or landslides, for instance.

 

This research is carried out as part of the S2S-FUTURE European Marie Skłodowska-Curie ITN (grant agreement No 860383).

 

Rush et al. (2021) Palaeogeography, Palaeoclimatology Palaeoecology, 568. doi: 10.1016/j.palaeo.2021.110289

Chen et al. (2018) Scientific Reports. doi: 10.1038/s41598-018-31076-3