A two-stage river capture event in Corsica and its impact on erosion rates and offshore sedimentation

The source-to-sink system of the Golo River, the largest catchment of Corsica (Western Mediterranean) is a well-established test case for inferring erosion rate variations from the sedimentary record in a quiescent tectonic setting. Previous studies have analyzed the onshore part of the source-to-sink system during late Quaternary climatic and sea level variations, and the offshore sink to highlight the main variations in sediment yield during the late Pleistocene and the last glacial cycle. Here we expand the analysis of the river network of Corsica and of the offshore sink back to the Miocene, when the region was still tectonically active. Based on a unique set of geological and in situ ¹⁰Be cosmogenic data, we show how the landscape have responded and is still responding to the disequilibrium caused by the late Miocene uplift of Alpine Corsica, and we provide evidence of a two-stage river capture event affecting the river network during the Pliocene. Our data reveal that ~1280 km² of basin area originally draining towards the Ligurian Sea was abruptly connected in the Pliocene to the Tyrrhenian Sea through headward erosion. River capture led to the formation of a large Pliocene-Quaternary submarine fan offshore the Tyrrhenian coast, associated to an increased sediment yield that was three times greater than the average sediment yield in the same source-to-sink system during the Holocene. Such a major change in sediment flux towards the Tyrrhenian margin was greater magnitude than any subsequent peaks in sediment yield documented during Pleistocene glaciations. In situ ¹⁰Be cosmogenic data demonstrate that erosion is focused on previous capture sites even today, which indicates persistence of disequilibrium after millions of years. Our findings suggest that using the sedimentary archive to infer tectonic growth of topography or climate changes is not straightforward and may lead to incorrect interpretation unless river piracy can be safely excluded.