Reconciling Geologic and Paleotopographic Constraints on Source-to-Sink Sediment Fluxes: An Example From the Bartonian Pyrenees

Abstract

Estimations of source-to-sink sediment fluxes over geological timescales allow a better understanding of landscape sensitivity to forcings such as climate or tectonics. The Pyrenees Mountains represent an ideal location to test the accuracy of source-to-sink predictive methods, as the well-studied mountainous sources and sediment sinks, including the Aquitaine, Jaca, and Ebro basins, collectively serve as a reference for evaluating the accuracy of predictive approaches. This study uses a paleo-digital elevation model (pDEM) of Bartonian age (ca. 40 Ma) to reconstruct catchments for the Pyrenees. When coupled with published paleoclimatic constraints, the BQART equation is used to predict sediment fluxes into each sedimentary basin. Predicted sediment volumes are compared against volumes calculated from bedrock exhumation rates across the Pyrenees, and against published rock volumes preserved within Pyrenean sedimentary basins. Consistency between total sediment volumes predicted by the BQART model and for exhumation rates is within a factor of 1.5, and within a factor of 2 when sediment volumes are partitioned by sedimentary basin, indicating the pDEM is able to generate realistic, first-order estimates of sediment flux. An uncertainty analysis showed that the runoff category contributes the greatest uncertainty to the BQART equation, highlighting the requirement for paleoclimate and drainage constraints on this parameter. When BQART and exhumation-derived volumes are compared against preserved sediment volumes in the Aquitaine and Jaca Basins, sediments are undercounted by an order of magnitude. This is a result of the limited scope of volume quantification, as depocentres are defined by modern geography only, and from the postdepositional erosion of sediment in an active orogenic setting. Sediment volumes in the better-preserved Ebro Basin were predicted within a factor of 1.35 and 2.5. The results show that the pDEM-BQART method can appraise both the completeness of the sedimentary record within depocentres and successfully elucidate source-to-sink sediment routing within ancient orogens.