Detrital zircon mixing and sediment-routing partitioning from rivers to coastal and canyon–fan systems along the Colombian Caribbean margin

The tectonically active northern Colombian Caribbean margin, where the Magdalena Canyons System (MCS) lies adjacent to the structurally confined La Aguja Canyon (LAC), provides an exceptional natural laboratory to investigate sediment mixing and the partitioning of transport pathways between coastal and deep-marine environments. Here, we integrate new detrital zircon U–Pb geochronology from 18 coastal and offshore samples (~1,900 grains) with published river and coastal datasets to assess how provenance signals are transferred from onshore sources through submarine canyon systems into offshore depocenters. Detrital zircon ages span from <1 Ma to ~2700 Ma.

Our dataset includes 10 offshore samples distributed across the MCS, LAC, and distal sectors of the Magdalena Submarine Fan, together with 8 newly analyzed coastal samples. The coastal samples capture sediment supplied by two contrasting source regions: the Magdalena River, which delivers the largest sediment load to the Caribbean and carries a characteristically multimodal Andean-derived zircon signature, and rivers draining the Sierra Nevada de Santa Marta (SNSM), which provide a lower sediment flux but a compositionally distinct crystalline signal directly to the coast. All samples were analyzed using detrital zircon U–Pb geochronology (LA-ICP-MS), complemented by grain-size analysis, cathodoluminescence imaging, and bulk mineralogical characterization by X-ray diffraction. Detrital zircon U–Pb age distributions were evaluated using kernel density estimates, multidimensional scaling, and inverse mixing models.

River and coastal datasets define two robust provenance end members. Sediments associated with the Magdalena River exhibit a multimodal Andean-derived age spectrum characterized by Neogene–Quaternary (<8 Ma), Jurassic–Cretaceous (~75–180 Ma), and Neoproterozoic (~990 Ma) populations. In contrast, sediments sourced from the SNSM display a narrower Paleogene–Jurassic–Proterozoic spectrum, with prominent peaks at ~50 Ma, ~180 Ma, and ~990 Ma. Offshore samples reflect this partitioning across distinct canyon domains: MCS samples retain the multimodal Magdalena signature, whereas LAC samples preserve the restricted SNSM signal. Distal fan samples integrate both age populations, delineating a downslope mixing zone where sediment contributions from both canyon systems may converge. Statistical analyses consistently support this sediment-routing partitioning, indicating dominant Magdalena-derived input to the MCS and distal fan, and a strongly confined SNSM signal within the LAC with limited distal transfer.

These results demonstrate that sediment routing along the northern Colombian Caribbean margin is strongly partitioned between adjacent submarine canyon systems, yet becomes progressively integrated downslope within the Magdalena Submarine Fan. While Magdalena-derived sediments are routed through the MCS and SNSM-derived material remains largely confined within the LAC at proximal and canyon scales, their provenance signals converge and mix within distal fan depocenters. This transition from canyon-scale partitioning to fan-scale mixing, controlled by tectonic confinement, source-area configuration, and canyon morphology, illustrates how sediment-routing systems operate in tectonically complex, actively deforming continental margins worldwide.

Keywords: detrital zircon U-Pb geochronology, source-to-sink systems, submarine canyons, marine sediment provenance, Caribbean margin